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handout4_filled - Structural Biochemistry TA Phu Tran...

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Structural Biochemistry Dr. Lukas Buehler TA Phu Tran pdtran@ucsd.edu Sections A03 W 1 - 3 pm Solis 111 OH after class by appointment Handout 4 Enzymes Enzymes are biological catalysts, usually made of amino acids, that speed up reaction rates. They lower the _ activation _ or _ transition _ state energy threshold required for the reaction to go in a certain direction. They _ stabilize _ the transition state over the initial state of the substrate. Carbonic _ anhydrase _ is the fastest enzyme in the human body, involved in fixing carbon dioxide into carbonic acid for transport within the circulatory system. The Michaelis-Menten equation describes the kinetics of many enzymes wherein the [enzyme] is much lower than the [substrate] so that [enzyme] is the limiting factor. S K S V v M o + × = max To determine the maximum rate of an enzyme-mediated reaction, a series of experiments is carried out where the substrate concentration [S] is increased until a constant initial rate of product formation is achieved. This is the maximum velocity (V max ) of the enzyme under the conditions of the experiment. In this state, enzyme active sites are _ saturated _ with substrate. The reaction rate V is the number of reactions per second catalyzed per mole of the enzyme. Since the curve is asymptotic to V max , ½ V max is more useful to characterize an enzyme. The [Substrate] at which ½ V max is achieved is called K M , or the Michaelis constant. In a double reciprocal _ Lineweaver _ - _ Burk _ plot, the equation is rewritten as shown below. The curve is a straight line with X- intercept -1/K M and Y-intercept 1/V max . The slop of the curve is K m /V max . Notice the axes are both reciprocals instead of straight values. [Substrate] to reach V
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handout4_filled - Structural Biochemistry TA Phu Tran...

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