Principles of Biochemistry/Enzymes - Wikibooks, open books for an open world
of Enzymes Definition. Different Types of Enzyme Specificity: Bond, Group, Substrate, Stereo Specificity. Biochemistry of Enzyme Substrate Specificity and its Classification With Examples.“There is more to life . Related posts: Enzyme . An intimate relationship of this kind between the interacting groups, suitably arranged in space, of enzyme and substrate may be regarded as the material basis. Substrate specificity is another important enzyme property. on finding an enzyme with a low level of activity or an enzyme that acts upon a related substrate.
Absolute specificity[ edit ] Absolute specificity can be thought of as being exclusive, in which an enzyme acts upon one specific substrate.
For example, lactase is an enzyme specific for the degradation of lactose into two sugar monosaccharides, glucose and galactose. Another example is Glucokinasewhich is an enzyme involved in the phosphorylation of glucose to glucosephosphate. It is primarily active in the liver and is the main isozyme of Hexokinase. Group specificity[ edit ] Group specificity occurs when an enzyme will only react with molecules that have specific functional groups, such as aromatic structures, phosphate groups, and methyls.
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Another example is hexokinase, an enzyme involved in glycolysis that phosphorylate glucose to produce glucosephosphate. This enzyme exhibits group specificity by allowing multiple hexoses 6 carbon sugars as its substrate. Bond specificity[ edit ] Bond specificity, unlike group specificity, recognizes particular chemical bond types.
Figure 1 is a reaction that illustrates an enzyme cleaving a specific bond of the reactant in order to create two products. This differs from group specificity, as it is not reliant on the presence of particular functional groups in order to catalyze a particular reaction, but rather a certain bond type for example, a peptide bond.
Stereochemical molecules differ in the way in which they rotate plane polarized light, or orientations of linkages see alpha, beta glycosidic linkages. Enzymes that are stereochemically specific will bind substrates with these particular properties.
For example, beta-glycosidase will only react with beta-glycosidic bonds which are present in cellulose, but not present in starch and glycogen, which contain alpha-glycosidic linkages.
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This is relevant in how mammals are able to digest food. For instance, the enzyme Amylase is present in mammal saliva, that is stereo-specific for alpha-linkages, this is why mammals are able to efficiently use starch and glycogen as forms of energy, but not cellulose because it is a beta-linkage.
Determining chemical specificity[ edit ] kd, is known as the specific equilibrium dissociation constant for formation of the enzyme-substrate complex.
Application to enzyme kinetics[ edit ] The chemical specificity of an enzyme for a particular substrate can be found using two variables that are derived from the Michaelis-Menten equation. Also known as the efficiency of an enzyme, this relationship reveals an enzyme's preference for a particular substrate.
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The higher the specificity constant of an enzyme corresponds to a high preference for that substrate. Key concepts Specificity is most manifest in the rate that a substrate reacts rather than the affinity of substrate binding. A good substrate can induce an active enzyme conformation that is not accessed by a poor substrate.
Some enzymes contain additional active sites that catalyse proofreading reactions, further enhancing specificity. The hydrolysis of peptide bonds.
Enzyme Specificity and Selectivity
Note that the active site is complementary to the transition state, providing hydrogen bonds to stabilize the oxyanion. Fidelity in the DNA polymerase reaction. Discrimination at the level of incorporation favours the correct nucleotide by a factor of The correct nucleotide triphosphate induces the active conformation and is efficiently incorporated into the growing DNA strand.
The incorrect nucleotide triphosphate induces a less active conformation and is inefficiently incorporated.Enzymes
DNA polymerase also has a proofreading mechanism that selectively removes the incorrect nucleotide, also by a factor of Together, these two mechanisms account for the extraordinary fidelity of DNA replication.
The lactate dehydrogenase reaction. When the enediol is formed in solution, elimination of the phosphate occurs to produce methylglyoxal. On the enzyme, the phosphate is held in the plane of the double bond to prevent the elimination reaction. The carbanion is formed by removal of the group perpendicular to the plane of the ring.