Chapter05FALL05 - Chapter 5 Properties of Enzymes...

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Chapter 5 - Properties of Enzymes Characteristics of enzymes 1) biological catalysts 2) not consumed during a chemical reaction 3) speed up reactions from 1000 - 10 17 , with a mean increase in rate of 00,000 4) exhibit stereospecificity --> act on a single stereoisomer of a substrate 5) exhibit reaction specificity --> no waste or side reactions Nomenclature Typically add “-ase” to name of substrate e.g. lactase breaks down lactose (dissacharide of glucose and galactose) IUBMB classifies enzymes based upon the class of organic chemical reaction catalyzed: 1) oxidoreductase - catalyze redox reactions dehydrogenases, oxidases, peroxidases, reductases 2) transferases - catalyze group transfer reactions; often require coenzymes 3) hydrolases - catalyze hydrolysis reactions 4) lyases - lysis of substrate; produce contains double bond 5) isomerases - catalyze structural changes; isomerization 6) ligases - ligation or joining of two substrates with input of energy, usually from ATP hydrolysis; often called synthetases or synthases Enzyme kinetics: A mathematical and graphical study of the rates of enzyme-catalyzed reactions. k S -----------> P k A + B ---> C The velocity of this reaction can be summarized by the following equation: v = k[S] or v = k[A][B] This reaction is considered a first order reaction , determined by the sum of the exponents in the rate equation --> number of molecules reacting. There are also bimolecular reactions , which involve two substrates; good example of group transfer reactions.
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S 1 + S 2 ---> P 1 + P 2 v = k[S 1 ][S 2 ] first order for each reactant; but second order overall For enzyme-catalyzed reactions: E + S -----> ES -----> E + P The rate or velocity is dependent upon both [enzyme] and [substrate]. In reality, enzyme-catalysed reactions are not that simple: k 1 k cat E + S ES E + P k -1 k 1 and k -1 govern the rates of association and dissociation of ES k cat is the turnover number or catalytic constant
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Chapter05FALL05 - Chapter 5 Properties of Enzymes...

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