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Enzyme Kinetics Bwahahahaha!

Enzyme Kinetics Bwahahahaha!. Ribozymes. Saturation kinetics. Assumptions in the Henri-Michaelis-Menton Equation. formation of an enzyme-substrate complex ES complex is in rapid equilibrium with free enzyme Breakdown of ES to form products is assumed to be slower than

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Enzyme Kinetics Bwahahahaha!

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  1. Enzyme KineticsBwahahahaha!

  2. Ribozymes

  3. Saturation kinetics

  4. Assumptions in the Henri-Michaelis-Menton Equation • formation of an enzyme-substrate complex • ES complex is in rapid equilibrium with free enzyme • Breakdown of ES to form products is assumed to be slower than 1) formation of ES and 2) breakdown of ES to re-form E and S

  5. Michaelis-Menton Equation is a Combination of 0-order and 1st-order kinetics • When S is low, the equation for rate is 1st order in S • When S is high, the equation for rate is 0-order in S • The Michaelis-Menten equation describes a rectangular hyperbolic dependence of v on S!

  6. Be able to derive it!

  7. Assumptions in the Henri-Michaelis-Menton Equation • formation of an enzyme-substrate complex • ES complex is in rapid equilibrium with free enzyme • Breakdown of ES to form products is assumed to be slower than 1) formation of ES and 2) breakdown of ES to re-form E and S • Under ‘steady-state’ conditions d[ES]/dt = 0

  8. The Michaelis constant • Km is a constant • Km ≠KD • Km is derived from rate constants • Km is, under true Michaelis-Menten conditions (k2 is small), an estimate of the dissociation constant of E from S • Small Km means tight binding; high Km means weak binding

  9. What is Vmax? • Vmax is a constant • Vmax is the theoretical maximal rate of the reaction - but it is NEVER achieved in reality • To reach Vmax would require that ALL enzyme molecules are tightly bound with substrate • Vmax is asymptotically approached as substrate is increased • If k2 is rate limiting, v = k2[ES]. At saturation, [ES] = [E]total and Vmax = k2[E]total

  10. http://www.wellesley.edu/Biology/Concepts/Html/vmaxfrommme.htmlhttp://www.wellesley.edu/Biology/Concepts/Html/vmaxfrommme.html

  11. kcat, the turnover number, is the number of substrate molecules converted to product per enzyme molecule per unit of time, when E is saturated with substrate. • If the M-M model fits, k2 = kcat = Vmax/Et • Values of kcat range from less than 1/sec to many millions per sec

  12. Catalytic efficiency • An estimate of "how perfect" the enzyme is • kcat/Km is an apparent second-order rate constant • It measures how the enzyme performs when S is low • The upper limit for kcat/Km is the diffusion limit - the rate at which E and S diffuse together

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