Metabolic Biochemistry notes

Metabolic Biochemistry notes - Metabolic Biochemistry...

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Metabolic Biochemistry Enzyme Kinetics - S>P, Keq = [P]/[S] - Rate of any reaction determined by a rate constant usually denoted by “k”. - For the reaction S>P, the velocity V representing the amount of S that reacts per unit time is expressed by V=k[S]. Since in this reaction the rate only depends on the concentration of S, this is called a first-order reaction - Binding energy: formation of each weak interaction in the ES complex is accompanied by release of a small amount of free energy that provides a degree of stability to the interaction. Binding energy is a major source of free energy used by enzymes to lower the activation energies of reactions - A good enzyme does not perfectly fit a substrate, but rather stabilizes the transition state. - Rate-limiting step – The step with the highest activation energy - For enzyme kinetics, a key factor affecting the rate of a reaction is the concentration of substrate, [S], but because [S] changes during an in-vitro reaction as it is converted into product, a simple approach is to measure Vo, or the initial rate, when [S] is much greater than [E]. - At high substrate concentrations, Vo increases by smaller and smaller amounts in response to increases in [S]. - Vmax is observed when virtually all the enzyme is present as the ES complex and [E] is vanishingly small. - During the steady state, [ES] remains constant. - Steady-state assumption – the rate of formation of ES is equal to the rate of its breakdown - Vo = k2[ES] - When k2 is the rate limiting step and Km reduces to k-1/k1, which is the dissociation constant, Kd, of the ES complex, Km represents a measure of the affinity of the enzyme for its substrate in the ES complex. - Kcat = limiting rate of any enzyme-catalyzed reaction at saturation - Competitive Inhibitor – Means that Vmax (the maximum speed the reaction goes with all the enzymes used) is the same, but Km changes (where you see half max velocity), because this active site is having to compete (competitive inhibitor) with the inhibitor. With competitive inhibitors, you can add enough substrate to completely out-compete the inhibitor. - Noncompetitive inhibitor – When a molecule binds to an allosteric site alters the conformation of enzyme so that the active site goes away, therefore substrate can’t bind. Vmax is lowered. Non-reversible. Km stays the same though. -
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This note was uploaded on 02/06/2009 for the course BIBC BIBC 102 taught by Professor Price during the Fall '08 term at UCSD.

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Metabolic Biochemistry notes - Metabolic Biochemistry...

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