Enzymes I

Enzymes I - Enzymes Enzyme Basics Definition - biological...

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1 Enzymes Enzyme Basics • Definition - biological catalysts (almost all are globular proteins) • Highly specific (substrate specific, stereospecific, etc) • Often highly regulated • Enzymes increase reaction rate – Decrease E a – No change in Δ G Kinetics vs. Thermodynamics • Thermodynamics – Deals with change in system energy ( Δ G) Δ G is the ultimate measure of favorability (spontaneity) Δ G issues can be dealt with by reaction coupling (more on this later) – Negative Δ G = favorable/spontaneous, but these reactions may still be SLOW
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2 Kinetics vs. Thermodynamics • Kinetics – Deals with reaction rate (E a ) – Lower E a = faster reaction • This issue is of great importance to living systems! – E a issues can be dealt with by catalysts – Catalysts change pathway, but not energy • They speed up forward and reverse reactions • Often, they stabilize transition states or provide alternatives for logistically difficult steps in a mechanism Classification of Enzymes • Oxidoreductase: redox reactions – dehydrogenase, oxidase, reductase… – Example: alcohol dehydrogenase CH 3 CH 2 OH + NAD + H O + NADH + H + Classification of Enzymes • Transferase: group transfer reactions – aminotransferase, methyltransferase… – Example: hexokinase O OH OH OH OH CH 2OH O OH OH OH OH CH 2O ATP ADP P
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3 Classification of Enzymes • Hydrolase: hydrolysis reactions – esterase, phosphatase, peptidase… – Example: PDE-5, a cGMP phosphodiesterase HN N N O H2N N O OH O O P
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This note was uploaded on 04/28/2009 for the course BCH 361 taught by Professor Fromme during the Spring '08 term at ASU.

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Enzymes I - Enzymes Enzyme Basics Definition - biological...

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