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SPECIAL REVIEW TOPIC: ENZYMES AND

SPECIAL REVIEW TOPIC: ENZYMES AND . ENERGETICS ENZYMES ARE CATALYSTS THAT LOWER ACTIVATION ENERGY AND ASSIST REACTIONS TO OCCUR

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SPECIAL REVIEW TOPIC: ENZYMES AND

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  1. SPECIAL REVIEW TOPIC: ENZYMES AND • ENERGETICS • ENZYMES ARE CATALYSTS THAT LOWER ACTIVATION ENERGY AND ASSIST REACTIONS TO OCCUR • THE ACTIVE SITE CONISTS OF SPECIFIC SIDE CHAIN GROUPS WHICH ARE BROUGHT INTO CONFROMATION BY FORCES OF ELECTROSTATIC BONDING, VAN DER WAALS FORCES, HYDROGEN BONDING • MANY IONIZABLE SIDE GROUPS ARE EXPOSED IN THE ACTIVE SITE. THIS MAY HELP THE BINDING PROCESS

  2. ENZYMES MAY EXERT THE FOLOWING ACTIVITIES: • MAY HOLD REACTANTS IN A SPECIFIC ORIENTATION • MAY REACT DIRECTLY WITH SUBSTRATE TO FORM UNSTABLE INTERMEDIATE THAT RAPIDLY ENTERS INTO SECOND REACTION AND YIELDS PRODUCT

  3. ENZYMES MAY EXERT THE FOLOWING ACTIVITIES: • SIDE GROUPS MAY ACT AS PROTON DONORS AND ACCEPTORS AND FACILITATE ACID-BASE REACTIONS • BINDING MAY CAUSE BBOND STRESS, INCREASING PROBABILITY BONDS WILL BREAK AND FACITITATE REACTION

  4. TEMPERATURE AND ACID –BASE STATUS ARE IMPORTANT FACTORS • COFACTORS ARE USUALLY NECESSARY • ALLOSTERIC ACTIVATION OR INHIBITION CAN OCCUR

  5. ENZYME KINETICS • THE RATE AT WHICH A REACTION PROCEEDS IS DEPENDENT UPON THE CONCENTRATION OF ACTIVE ENZYME, SUBSTRATE AND PRODUCT • RATE OF CONVERSION • WHERE: [A]= INSTANTANEOUS CONCENTRATION OF SUBSTRATE K= rate constant -d[A]/dt = RATE AT WHICH A IS CONVERTED TO P

  6. FIRST ORDER REACTION =WHEN RATE OF CHANGE OF A QUANTITY IS PROPORTIONAL TO THE INSTANTANEOUS VALUE OF THE QUANTITY THERE ARE ALSO ZERO ORDER AND SECOND ORDER KINETICS

  7. ENZYME SUBSTRATE AFFINITY • THE MAXIMUM RATE OF A REACTION ( VMAX) OCCURS WHEN ALL AVAILABLE ENZYME IS SATURATED WITH SUBSTRATE. THE ENZYME IS RATE LIMITING IN THIS CASE • ENZYMES DIFFER IN THEIR TURNOVER NUMBERS SO VMAX VARIES DEPENDENT ON THE GIVEN CONSTITUENTS

  8. Michaelis-menten Eqn For Rate Of A Single Enzyme Catalyzed Reation:

  9. WHERE: • Vo = initial reaction rate at substrate concentration [S] • Vmax= RXN RATE WITH EXCESS SUBSTRATE • Km= Michaelis- Menten constant; it depends on the affinity of the enzyme for the substrate- greater the affinity the lower the Km ; 1/Km is a measure of affinity of enzyme for substrate

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