# 16 - Friday October 1 2010 Lecture 16 Announcements 1 Quiz...

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Friday, October 1, 2010, Lecture 16 Announcements: 1. Quiz 4 results: A 25.7 B 23.7 C 23.8 2. Today at 2:55PM in Comstock B108: "Graduate school: What is expected of you, and what are your career options after your degree?” 3. Panel discussion re treatment of infants with ambiguous sex: Hollis E. Cornell Aud, 132 Goldwin Smith, Mon. 10/4 from 5:00 - 6:30PM Wednesday’s lecture: Some properties of the Michaelis-Menten Equation How to measure Km and Vm by use of the Lineweaver-Burk (double-reciprocal) plot The ES dissociation constant K S = k -1 /k 1 An elementary rate constant corresponds to one energy barrier to reach a transition state Today’s lecture: Page 116, details of how to go from kinetic data to the Lineweaver-Burk plot: 1. Calculate the reciprocals . Initially the data are in the form V in vs [S]. 2. Graph the reciprocals . 3. Extrapolate the straight line to reach the intercept at 1/V in = 0.0 on the x-axis. For the example on page 116, you determine that 1/V M = 100 M -1 min. Thus V M = 0.01 M min -1 . 4. Then, extrapolate to the x-axis to find: -1/K M = -200 M -1 , thus K M = 1/200 M -1 = 0.005 M In summary, using the Lineweaver-Burk plot requires either graph paper and a straight edge, or proper use of a calculator, or plotting and analysis using e.g. Excel. But note that on an exam, you will have graph paper and no access to Excel. Page 117 Turnover number is the number of substrate molecules converted to product per unit time when enzyme is saturated with substrate. This corresponds to k cat , V m = k cat [E] total Notice that k cat is used, not k 2 , because this rate constant might be more complex than a simple elementary rate constant. Turnover number (actually, its reciprocal) is the answer to the question, “How much time passes, once substrate has bound, until the chemical rxn is completed?”.

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Look at the table at the top right of page 117. The first enzyme, carbonic anhydrase, has a turnover number of 6x10 5 sec -1 . Wow, fast! This number is the k cat . Consider
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16 - Friday October 1 2010 Lecture 16 Announcements 1 Quiz...

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