lec 14 - BL/CH401 Lecture 13 Enzyme Kinetics Part II Enzyme...

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BL/CH401 Lecture 13 -- Enzyme Kinetics Part II. Enzyme Inhibition I. Basic Enzyme Kinetics For an enzyme obeying the Michaelis-Menten equation: Figure 1. Vmax and Km describe the catalytic properties of the enzyme. The meaning of Km is related to the affinity of the substrate for the enzyme. If Km has a very low concentration - substrate has a high affinity for the enzyme. Vo = Vmax at very high [S]. Vmax has units same as Vo (mmoles product/min) Km is [S] when Vo = Vmax/2. Km has units same as [S] (mM) Vmax is relative to total enzyme used. Vmax = kcat [E] kcat = catalytic rate constant kcat is called the turnover number kcat = substrate moles reacted/mole of enzyme/second Since [E] is difficult to determine, Vmax/Km is useful. Vmax/Km measures enzyme efficiency and all enzymes can be compared by using it. II. Enzyme Inhibitors. A. Competitive Inhibition Inhibitors of enzymes: Two types are considered - Competitive and Non-Competitive. A Competitive Inhibitor has a chemical similarity to the substrate and competes with the substrate for binding to the active site of the enzyme. A good example to describe competitive inhibition is the mitochondrial enzyme, succinate dehydrogenase:
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Figure 2. (A) The reaction catalyzed by succinate dehydrogenase is the oxidation of succinate to fumarate. (B) Malonate and oxaloacetate are competitive inhibitors of succinate dehydrogenase. Both these competitive inhibitors, malonate and oxaloacetate, look like succinate in their chemical character. Both inhibitors are dicarboxylic acids like the substrate succinate so they have groups which can bind in the same places in the active site of succinate dehydrogenase as the substrate. However, neither inhibitor has the capacity to undergo the reaction and so the enzyme is inhibited. Since these inhibitors simply bind to the enzyme, when the succinate concentration is high, they will be pushed out of the site by the substrate and the enzyme will catalyze the reaction as if no inhibitor were present. An enzyme mechanism model of the action of a competitive inhibitor (Ic) based on the standard
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This note was uploaded on 09/02/2009 for the course BIO BL 401 taught by Professor Wilbur during the Spring '07 term at Michigan Technological University.

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lec 14 - BL/CH401 Lecture 13 Enzyme Kinetics Part II Enzyme...

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