Chiral materials are optically active; the different forms affect light in different ways. See Chapter 3 for more on what makes a molecule chiral. The arrangement of the groups around a chiral carbon atom is important. Just as your left hand only fits into your left glove, only certain arrangements of the groups will fit because of what is called handedness. There are two different forms of the chiral amino acids: the D- and the L- forms.
Only the L- forms are constituents of proteins. The D- forms appear in some antibiotics and in the cell walls of certain bacteria. Fischer projections, as we explain in Chapter 3, are commonly used to represent the arrangement about the chiral carbon. Figure illustrates some different ways to draw the Fischer projections of the structure of amino acids. In these cases, there are four possible isomers.
Biological activity is usually limited to only one of these four isomers. In the following section we examine the structures of the individual amino acids. It is possible to represent each of the amino acids by either a threeletter or a one-letter abbreviation. Like the chemical symbols for the elements, these are fixed abbreviations. The three-letter abbreviations are easier to relate to the name of the specific amino acid.
For example, we use glu for glutamine. The one-letter abbreviations are shorter, but not always related to the name. For example, we use Q for glutamine. Tryptophan is a borderline case because the —NH from the ring system can interact with water to a limited extent. For this reason, they are usually more soluble than the nonpolar amino acids.
The amide, alcohol, and sulfhydryl —SH groups of the remaining members of this group are very polar and neutral. At very high pH values, the phenolic group on tyrosine ionizes to yield a polar charged group.
Figure shows these amino acids. This secondary carboxylic acid group is a weaker acid higher pKa than the primary carboxylic acid group. The carboxylate side chain is important in the interaction of many proteins with metal ions, as nucleophiles an electron-rich group replacing some group attached to a carbon in many enzymes, and in ionic interactions. This is especially true of histidine. In all three of these amino acids, there is a basic group capable of accepting a hydrogen ion.
In the case of lysine, this is a simple ammonium ion. Arginine forms the guanidinium group. Histidine forms an imidazolium group. As in the case of the acidic side chains, these side chains have a pKa value. Both arginine and lysine are usually protonated at physiological pH values.
In proteins, this net charge may be part of an ionic interaction. The pKa of the side chain of histidine is lower than other basic groups. Protonation of histidine becomes significant at much lower pH values. In many proteins, histidine is not protonated, but is important in many enzymes in hydrogen ion transfer processes. Figure shows these basic amino acids.
Lest We Forget: Rarer Amino Acids In a few cases, an amino acid may undergo modification once it is incorporated into a protein. Collagen and gelatin, for example — proteins present in higher vertebrates — contain hydroxylysine and hydroxyproline. These two amino acids contain an additional —OH group on the side chain. NH histidine Certain amino acids do not occur in proteins. Citrulline is the amino acid that serves as a precursor of arginine.
Ornithine, homocysteine, and homoserine are important as metabolic intermediates. Figure shows a couple of these amino acids. Rudiments of Amino Acid Interactions Amino acids are the ingredients used in the recipe in making a protein. Just as the individual ingredients in a recipe lead to distinct characteristics of what eventually shows up on the dinner table, the amino acids present contribute properties to proteins.
And just as you cannot replace the flour in a recipe with pepper, you generally cannot replace one amino acid in a protein with another. In both cases, the final product will be different. In the next section, we show you some of the ways that amino acids interact. These interactions set the stage for our discussion of bonding among the amino acids. HC C OH OH CH2 NH2 hydroxylysine Intermolecular forces: How an amino acid reacts with other molecules Amino acids can interact with other molecules — and we mean any other molecules, including fluids, other amino acids, and other biological molecules — in a variety of ways.
We cover intermolecular forces in general in Chapter 3, but in this section we show you how they play out when amino acids are involved. The carboxylic acid and amine parts of the amino acids define much of the reactivity of the molecule, but the side chains can also interact with other molecules. There are three general ways in which they can interact.
Nonpolar groups tend to clump together and exclude not only water but also all other types of side chains. The presence of a number of these groups increases the solubility of a protein. These groups hydrogen bond not only to water but also to each other. A carboxylate group from one side chain is attracted to the ammonium ion of another side chain through an ionic interaction.
This ionic bond is very strong. The amino acid cysteine can interact with a second cysteine molecule through a different type of interaction Figure The mild oxidation of two cysteine sulfhydryl groups leads to the formation of cystine. A disulfide linkage joins the two amino acids with a covalent bond. Mild reduction can reverse this process. The greater the number of disulfide linkages, the curlier the hair! If you change the pH, you change some of the interactions.
In this section we show how those changes affect interactions involving amino acids. Just like any other molecule, an amino acid has two or three functional groups, depending on the amino acid. Those functional groups include those with oxygen and sulfur, those with nitrogen, and those with phosphorus.
A change in pH affects one to three of those functional groups in terms of interactions. So if an amino acid has a functional group that changes from a dipole-dipole interaction to an ionic interaction.
One example of the dipole-dipole to ionic interaction change is the process of milk curdling. If you add an acid to milk, it coagulates. Casein has an isoelectric point at 4. This works against the dipole-dipole interactions with water, so that the protein precipitates. The pKa values for the various groups present in the different amino acids are shown in Table At a lower pH, more than half is protonated, whereas at a higher pH more than half is deprotonated.
The pH dependence of the protonation of amino acids aids in their separation and identification. Because the amino acids use the carboxylic acid and amine ends when they join to form a protein, only the pKa values of the side chains are important in additional interactions and reactions. We cover the fundamentals about protein creation in Chapter 5, but before you dive into that topic, this section gives you a solid understanding of how two amino acids join together in the first place, and how additional amino acids link onto the chain gang.
The process is reversible as in digestion. When drawing the chemical structures of amino acids and their bonds, the standard convention is to first draw the structures from the ammonium group of the first amino acid the N-terminal residue , starting at the left, and continuing the drawing to the right, ending with the carboxylate group C-terminal residue of the last amino acid.
The peptide bond and the dipeptide One of the most important types of bonds in all of biochemistry is the peptide bond. As you will see, it is this type of bond that will be used in the synthesis of proteins. The reverse of this condensation reaction is hydrolysis. The resultant amide group is a peptide bond. The presence of two amino acid residues means the product is a dipeptide. It is stabilized by our old organic friend, resonance. Figure illustrates the stabilization.
The resonance increases the polarity of the nitrogen and oxygen. This increase in polarity leads to hydrogen bonds that are much stronger than most other hydrogen bonds. The double bond character between the carbon and the nitrogen restricts rotation about this bond.
Figure Resonance stabilization of a peptide bond. For example, combining glycine, alanine, and serine yields the illustration in Figure Notice that everything begins with the N-terminal residue and ends with the C-terminal residue. You could designate this tripeptide as gly-ala-ser using the three letter abbreviations. In the next chapter, we cover that topic in full.
They usually serve as structural entities — for example, connective tissue, tendons, and muscle fiber. They are normally insoluble in water. They are usually water-soluble. Hemoglobin, the protein that transports oxygen to the cells, is a transport protein. For example, iron is stored in the liver in a complex with the protein ferritin. The function that a particular protein assumes is, in many cases, directly related to the structure of that protein.
Proteins may have as many as four levels of structure key word being levels, not different structures , each of which places the components into a position where these intermolecular forces can interact most advantageously.
The levels are simply labeled primary, secondary, tertiary, and quaternary. Primary is the most fundamental level that all proteins have, and quaternary is the most specific level that only some proteins have. Intermolecular forces themselves are important to the function of a protein, of course, but the arrangement of the molecules is even more significant. In some cases, the process may be reversible.
Primary Structure: The Structure Level All Proteins Have The primary structure of a protein is simply the sequence of amino acids comprising the molecule. The primary structure of a protein is the amino acid sequence within the molecule. All proteins have a primary structure, because all proteins by definition consist of a sequence of amino acids. The primary structure serves as the foundation upon which all higher levels of protein structure build. Building a protein: Outlining the process During the synthesis of a protein, the chain of amino acids is built one link at a time, roughly as follows: 1.
The transfer RNA tRNA molecule transfers specific amino acids to the mitochondria of the cell to connect to the growing chain. Each amino acid joins to the chain through the formation of a peptide bond. See Chapter 4 for more on peptide bonds. The first peptide bond joins two amino acids to form a dipeptide.
The second peptide bond joins three amino acids to produce a tripeptide. This process continues hundreds, if not thousands, of times to produce a polypeptide — a protein. When two or more amino acids combine, a molecule of water is removed. What remains of each amino acid is called a residue. They lack a hydrogen atom on the amino group, or an —OH on the carboxyl group, or both. It is necessary to supply energy, as we will see later, to synthesize the protein.
Organizing the amino acids One end of the primary structure has an amino group, and the other end has a carboxylate group. Drawing, naming, numbering, and other treatments of the primary structure always begin with the amino end called the N-terminal and stop with the carboxylate end the C-terminal.
For example, in the hexapeptide Met-Thr-Ser-Val-Asp-Lys see Chapter 4 for a list of the amino acids and their abbreviations , methionine Met is the N-terminal amino acid, and lysine Lys is the C-terminal amino acid. Note that reversing the sequence to Lys-Asp-Val-Ser-Thr-Met also gives a hexapeptide with the same composition but with different chemical properties because you initially started with a different amino acid.
Therefore an amino acid that lost a hydrogen in one sequence will lose an —OH in the other. Variations take place in the form of side chains — the R groups of the amino acids. You can see this repeating sequence in Figure Notice that the repeating unit indicated by the brackets is the amino-carboncarbonyl sequence and that there can be different R groups attached to the carbon unit of this backbone.
Figure Repeating sequence of the protein backbone. Every residue — other than the amino acid proline — has an NH, which may serve as a donor to a hydrogen bond. And every residue has a carbonyl group, which can serve as the acceptor of a hydrogen bond.
The presence of donors and acceptors leads to the possibility of forming numerous hydrogen bonds. Each of the peptide bonds exhibits no free rotation about the carbon-nitrogen bond because of the contribution of the resonance form, which has a double bond. Thus, there is a planar unit of four atoms, and in almost all cases, the oxygen atom is trans to the hydrogen atom. The remainder of the backbone can rotate.
The ability to rotate or not influences how the three-dimensional structure of the protein is established. The rigidity of the peptide bond and rotation restrictions lower the entropy of the three-dimensional structure of a protein relative to a random chain of amino acids. Lowering the entropy helps stabilize the structure. Example: The primary structure of insulin The first determination of the primary structure of a protein was that of bovine insulin, the structure of which appears in Figure Since this landmark determination, the primary structures of more than , proteins have been determined.
In all cases, the protein has a unique primary structure. In general, the formation of these hydrogen bonds leads to the secondary structure of a protein.
The secondary structure is the result of many hydrogen bonds, not just one. The hydrogen bonds are intramolecular, that is between segments of the same molecule, as shown in Figure 5—3: Figure Hydrogen bonding between two peptide bonds.
Secondary structures may be only a small portion of the structure of a protein or can make up 75 percent or more. Each turn consists of 3. These turns allow hydrogen bonding between residues spaced four apart. Every peptide bond participates in two hydrogen bonds: one from an NH to a neighboring carbonyl, and one from a neighboring NH to the carbonyl Figure Structurally, the helices may be either right-handed or left-handed see Chapter 3 for more on handedness.
Essentially all known polypeptides are right-handed. Slightly more steric hindrance is present in a left-handed helix, and the additional steric hindrance makes the structure less stable.
A group of isoleucine residues disrupts the secondary structure because of the steric hindrance caused by their bulky R groups.
The small R group of glycine, only an H, allows too much freedom of movement, which leads to a destabilization of the helix. Other residues that destabilize the helix, for similar reasons, are lysine, arginine, serine, and threonine. Here, the primary structure is extended instead of tightly winding into a helix. Again, hydrogen bonds are the source of these structures.
The strands are different parts of the same primary structure. In the parallel structure, the adjacent polypeptide strands align along the same direction from N-terminal end to C-terminal end. In the anti-parallel structure, the alignment is such that one strand goes from N-terminal end to C-terminal end, while the adjacent strand goes from C-terminal end to N-terminal end Figure The hydrogen bonding pattern in the parallel structure is the more complicated.
Here, the NH group of one residue links to a CO on the adjacent strand, whereas the CO of the first residue links to the NH on the adjacent strand that is two residues down the strand. If the arrows point in the same direction, it is the parallel structure, and if they point in opposite directions, it is the anti-parallel structure. The sheets are typically 4 or 5 strands wide, but 10 or more strands are possible.
The arrangements may be purely parallel, purely anti-parallel, or mixed refer to Figure The hairpin bend is simply a bend in the primary structure held in place by a hydrogen bond. Both are found on the exterior of proteins. Nonpolar side chains are hydrophobic and, although repelled by water, are attracted to each other. Polar side chains attract other polar side chains through either dipole-dipole forces or hydrogen bonds. For example, both aspartic acid and glutamic acid yield side chains with a negative charge that are strongly attracted to the positive charges in the side chains of lysine and arginine.
Two cysteine residues can connect by forming a disulfide linkage — a covalent bond Figure Examination of the structures of many proteins shows a preponderance of nonpolar side chains in the interior with a large number of polar or ionic side chains on the exterior. In an aqueous environment, the hydrophobic nonpolar groups induce the protein to fold upon itself, burying the hydrophobic groups away from the water and leaving the hydrophilic groups adjacent to water. The result is similar in structure to a micelle.
These interactions include hydrogen bonding and disulfide bonds. This quaternary structure locks the complex of proteins into a specific geometry. An example is hemoglobin, which has four polypeptide chains. Dissecting a Protein for Study The previous sections have discussed the different types of protein structure.
Now it is time to see how a biochemist goes about determining the structure s of a particular protein. An animal generates an antibody in response to a foreign substance known as an antigen.
Antibodies are proteins found in the blood serum. Exposure to diseases, certain chemicals, and allergies induce the formation of specific antibodies. These antigens collect on the surface of red blood cells. Every antigen has a specific antibody. Antibodies are very specific and have a strong affinity for their specific antigens, recognizing specific amino acid sequences on the antigens. Animals have a large number of antibodies present in their bodies, based on their environmental history.
Separating proteins within a cell and purifying them There are thousands of different proteins in each cell. In order to examine and study one of them, you need to separate it from all the others. The methods of separating proteins are, in general, applicable to all other types of biochemicals. Initially, simple filtration and solubility can remove gross impurities, but much more needs to be done before the sample is pure.
The key separation and purification methods depend on two physical properties of the proteins: size and charge. Separating proteins by size Methods relying on separation by protein size and mass include ultrafiltration, ultracentrifugation, and size exclusion chromatography. Ultrafiltration can separate smaller molecules from larger impurities or larger molecules from smaller impurities.
In ultracentrifugation, a powerful centrifuge causes heavier molecules to sink faster and, which allows their separation — much as the lighter water is separated from the heavier lettuce in a salad spinner. Ultracentrifugation also gives the molar mass of the protein. In size exclusion chromatography, also known as molecular sieve chromatography or gel filtration chromatography, a solution passes through a chromatography column filled with porous beads. Molecules that are too large for the pores pass straight through.
Molecules that may enter the pores are slowed. The molecules that may enter the pores undergo separation depending on how easily they can enter. One of them is the examination of bloodstains, blood being the most common form of evidence examined by a forensic serologist. The presence of blood can link a suspect to both a victim and a crime scene. Bloodstain patterns can also give evidence of how a violent attack took place. Criminals recognize the significance of this evidence and often try to conceal it.
The luminol test is useful in detecting invisible bloodstains because, in contact with blood, or a few other chemicals, luminol emits light, which can be seen in a darkened room. The Wagenhaar, Takayama, and Teichman tests take advantage of the fact that long-dried blood will crystallize or can be induced to crystallize. Blood is mostly water, but it also contains a number of additional materials including cells, proteins, and enzymes.
The fluid portion, or plasma, is mostly water. The serum is yellowish and contains platelets and white blood cells. The platelets, or red blood cells, outnumber the white blood cells by about to 1. White blood cells are medically important, whereas red blood cells and, to a lesser extent, serum are important to the forensic serologist.
Because blood quickly clots when exposed to air, serologists must separate the serum from the clotted material. The serum contains antibodies that have forensic applications, and red blood cells have substances such as antigens on their surfaces that also have forensic applications. Antibodies and antigens are the keys to forensic serology: Even identical twins with identical DNA have different antibodies. As you know from this chapter, antibodies, and some antigens, are proteins, and this is why methods of studying proteins are important to their analysis.
The forensic investigator answers this question and the next one, if applicable by means of an antiserum test. It is important to know whether the blood came from a human or an animal such as a pet. The standard test is the precipitin test. If human antiserum creates clotting in a blood sample, the sample must be human. Analysis of bloodstains initially attempts to answer five questions.
To answer this question, the investigator can use a number of tests. The generic term for a test of this type is a presumptive test. It is possible to create animal antiserums in an analogous manner, and test for each type of animal.
The procedure for answering this depends on the quantity and quality of the sample. If the quality is good, direct typing is done — otherwise, indirect typing is used. A dried bloodstain normally requires indirect typing. The most common indirect typing method is the absorptionelution test. Treatment of a sample with antiserum antibodies gives a solution which, upon addition to a known sample, causes coagulation. Here the answers become less precise.
Clotting and crystallization indicate age. Testing for testosterone levels and chromosome testing can determine sex. And certain controversial, racial genetic markers based on protein and enzyme tests may indicate race. Other body fluids may contain the same antibodies and antigens found in blood.
Therefore, similar tests work on these fluids as well. Separating proteins by charge Methods of separating proteins relying on the charge of the protein include solubility, ion exchange chromatography, and electrophoresis. Each of these methods is pH dependent. Proteins are least soluble at their isoelectric point. The isoelectric point is the pH where the net charge on the protein is 0. At the isoelectric point, many proteins precipitate from solution.
At a pH below the isoelectric point, the protein has a net positive charge, whereas a pH above the isoelectric point imparts a net negative charge. The magnitude of the charge depends on the pH and the identity of the protein.
Therefore, two proteins coincidently having the same isoelectric point will not necessarily have the same net charge at a pH that is one unit lower than the isoelectric point. Both ion exchange chromatography and electrophoresis take advantage of the net charge.
In ion exchange chromatography, the greater the magnitude of the charge, the slower a protein moves through a column — this is similar to the ion-exchange process that occurs in water-softening units. In electrophoresis, the sample solution is placed in an electrostatic field. Molecules with no net charge do not move, but species with a net positive charge move toward the negative end, and those with a net negative charge move toward the positive end.
The magnitude of the net charge determines how fast the species moves. Other factors influence the rate of movement, but the charge is the key. There are numerous modifications of electrophoresis. In protein analysis, rarely do biochemists use only one single technique.
They commonly use several in order to confirm their findings. Because many proteins only have one polypeptide chain, this step is not always necessary.
Denaturing the protein, disrupting its threedimensional structure without breaking the peptide bonds, using pH extremes will normally suffice.
If disulfide linkages are present between the chains, apply the procedure outlined in Step 2 to separate the chains for isolation. Step 2: Slashing intrachain disulfide linkages Step 2 requires breaking cleaving the disulfide linkages. A simple reduction accomplishes this. However, the linkages may reform later, so it is necessary to cleave the linkages and prevent their reformation via reductive cleavage followed by alkylation.
Oxidative cleavage, where oxidation of the sulfur to —SO3— occurs, also prevents a reversal of the process. Step 3: Determining amino acid concentration of the chain Step 3 is easily accomplished using an amino acid analyzer, an automated instrument that can determine the amino acid composition of a protein in less than an hour. The instrument requires less than a nanomole of protein. Step 4: Identifying the terminal amino acids Step 4 not only identifies the terminal amino acids but also indicates whether more than one chain is present.
A polypeptide chain only has one N-terminal and one C-terminal amino acid. Therefore, if more than one N- or C-terminal amino acid is present, there must be more than one polypeptide chain. It is possible to identify the N-terminal residue in a number of ways. In general, procedures begin by adding a reagent that reacts with the N-terminal amino acid and tags it. Subsequent hydrolysis destroys the polypeptide, allowing separation of the tagged residue and its identification.
The method of choice nowadays is called the Edman degradation. This method, as do other methods, tags the N-terminal residue; however, only the terminal amino acid is cleaved from the chain, so the remainder of the chain is not destroyed as in other methods. It is possible to repeat the procedure on the shortened chain to determine the next residue. In principle, repetition of the Edman degradation can yield the entire sequence, but, in most cases, determination of the first 30 to 60 residues is the limit.
The akabori reaction hydrazinolysis and reduction with lithium aluminum hydride tag the C-terminal residue. It is also possible to selectively cleave the C-terminal residue using the enzyme carboxypeptidase, a variety of which are available.
Steps 5 and 6: Breaking the chain into smaller pieces In Step 5, you cleave the polypeptide into smaller fragments and determine the amino acid composition and sequence of each fragment. Step 6 repeats Step 5 using a different cleavage procedure to give a different set of fragments. Steps 5 and 6 break the chain into smaller pieces to ease identification.
Most of the methods here employ enzymes; however, other less-specific methods are useful in some cases. Partial acid hydrolysis randomly cleaves the protein chain into a number of fragments. Trypsin, a digestive enzyme, specifically cleaves on the C-side of arginine or lysine. Using trypsin gives additional information that the total number of arginine and lysine residues present is one less than the number of fragments generated.
The digestive enzyme chymotrypsin preferentially cleaves residues containing aromatic rings tyrosine, phenylalanine, and tryptophan. It slowly cleaves other residues especially leucine. Clostripain cleaves positively charged amino acids, especially arginine. It cleaves lysine more slowly. Fragments with a C-terminal aspartic acid or glutamic acid form from the interaction of staphylococcal protease on a protein in a phosphate buffer. In the presence of bicarbonate or acetate buffer, only C-terminal glutamic acid fragments result.
A number of less specific enzymes can complete the breakdown of the fragments, including elastase, subtilisin, thermolysin, pepsin, and papain. Chemical methods of breaking up the fragments include treatment with cyanogen bromide, hydroxylamine, and heating an acidic solution. Cyanogen bromide specifically attacks methionine.
Hydroxylamine specifically attacks asparagine-glycine bonds. It is possible to apply the Edman degradation on each of the fragments. This can simplify the determination of the sequence of a large protein. Step 7: Combining information to get the total sequence Step 7 is where the information from the various procedures comes together. For example, look at a simple octapeptide fragment from a protein. This fragment gave, upon complete hydrolysis, one molecule each of alanine Ala , aspartic acid Asp , glycine Gly , lysine Lys , phenylalanine Phe , and valine Val , and two molecules of cysteine Cys.
Over the years, additional reactions have been discovered. More than antigens are known, leading to 23 different blood groups. Each blood group is defined by the antibodies present in the serum and the antigens present on the red blood cells. In basic blood typing, one needs two antiserums, labeled anti-A and anti-B. Adding a drop of one of these to a blood sample causes coagulation if the appropriate antigens are present.
Anti-A interacts with both A and AB blood. Anti-B interacts with both B and AB blood. Neither interacts with type O blood. The approximate distribution of the different blood types is: 43—45 percent type O; 40—42 percent type A; 10—12 percent B; and 3—5 percent AB. Subgrouping is also possible with designations such as O1 and O2. There are other very rare types as well. The Rh factor provides an additional means of subdividing blood.
The Rh factor the name comes from the rhesus monkey is an antigen on the surface of red blood cells. A person with a positive Rh factor contains a protein antibody that is also present in the bloodstream of the rhesus monkey. About 85 percent humans are Rh positive. A person lacking this protein is, naturally, Rh negative. Assigning a blood sample as Rh positive or Rh negative is a useful simplification. There are about 30 possible combinations of factors.
Additional factors can determine whether blood belongs to a specific individual: the identification of other proteins and enzymes present in the blood. One of the characteristics of proteins or enzymes in the blood is polymorphism, or the ability to be present as isoenzymes. Polymorphism means that the protein may exist in different forms or variants. One well-known example is the polymorphism of hemoglobin into the form causing sickle cell anemia.
The determination of each of these additional factors narrows down the number of possible individuals. If the disulfide linkages are left intact by skipping Step 2, different fragments result. This can be used to determine the overall shape of a protein. In some cases, more detailed structural information can be determined by sophisticated instrumental analysis techniques.
As catalysts, they alter the rate of a chemical reaction without themselves being consumed in the reaction. Enzymes are normally very specific in their action, often targeting only one specific reacting species, known as the substrate.
This specificity includes stereospecificity, the arrangement of the substrate atoms in three-dimensional space. Stereospecificity is illustrated by the fact that if the D-glucose in your diet were replaced by its enantiomer, L-glucose, you would not be able to metabolize this otherwise identical enantiomer. Enzymes occur in many forms.
Some enzymes consist entirely of proteins, whereas others have non-protein portions known as cofactors. The cofactor may be a metal ion, such as magnesium, or an organic substance.
We call an organic cofactor a coenzyme there is no specific term for a metallic cofactor. An enzyme lacking its cofactor is an apoenzyme, and the combination of an apoenzyme and its cofactor is a holoenzyme. A metalloenzyme contains an apoenzyme and a metal ion cofactor.
A tightly bound coenzyme is a prosthetic group. We know that this is a lot of terminology, but hang in there. The key is the enzyme. If someone with copyrights wants us to remove this content, please contact us. Moreover Medstudentscorner. If you feel that we have violated your copyrights, then please contact us immediately. Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. From cell ultrastructure and carbohydrates to amino acids, proteins, and supramolecular structure, you'll identify biochemical structures and reactions, and send your grades soaring.
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