LEC 10[1] - Enzymes-bio catalysts, No effect of enzyme on...

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Enzymes-bio catalysts, No effect of enzyme on final equilibrium between substrate and product. Unlike chemical catalysts (platinum pilladium, where catalysts assembles on surface). Enzymes get regenarated when reaction is completed, they still maintain official property of catalysts. 1) no net change in composition 2) no effect on substrate-product equilibrium. The key is to lower the barrier, the activation energy. Refers to change of free energy going from substrate to transition state. Activation energy is most dramatically affected by enzyme. This is achieved by preferential stabilization of transition state . Substrate and product can bind to enzyme. In general, the affinity of enzyme for the transition state, is orders of magnitude greater then affinity for substrate or the product. If want to invent competitive inhibitor for enzyme and it was ok for inhibitor to compete, the best strategy is to make analogue for transition state. Those are transition state analogues . Although they are may be potent competitive inhibitors, there are conditions, where their competitive effect can be changed by high concentration of substrate . No matter how good of inhibitor they are, more concentration of substrate. Transition state analogues- great inhibitors, all enzymes bind preferentially transition states. Reaction proceeds normally with finite rate, going from substrate free energy to transition state free energy. Maybe difficult to see transition state. Catalysts affect the transition state free energy ( greatest effect ). Free enzyme and free substrate form enzyme-substrate complex, maybe non covalent association , binding of substrate to enzyme may have its own activation energy; this complex has lower free energy then free substrate or free enzyme. Therefore, this complex is preferential . Barrier provided for passing to the transition state is maximally lowered by having formed S-E complex, activation energy barrier for non catalyzed reaction is higher than from catalyzed one . The major effect of binding is to lower activation energy, that’s why reaction is speeded up by forming complex. Two fundamental energy differences: between final and initial state ( equilibrium change ), activation energy difference ( between uncatalyzed and enzyme catalyzed ) tells how much enzyme speeds at which equilibrium achieved, does not affect the value of equilibrium . This reaction is reversible. Position
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This note was uploaded on 01/30/2010 for the course BIO 351 taught by Professor Hoffmann,j during the Fall '08 term at SUNY Stony Brook.

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LEC 10[1] - Enzymes-bio catalysts, No effect of enzyme on...

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