MCB354_FA07_EXAM2_KEY - -1 mM l/Vo = 2.4 so V max = 0.42...

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MCB 354 Exam II 10/16/07 ANSWER KEY 1. (34 points total) You assay the activity of the enzyme chitin synthase at a range of substrate concentrations, and test whether the drug polyoxin inhibits the enzyme, You obtain the data in the table below, Assume that chitin synthase obeys Michaelis-Menten kinetics, Answer parts a, b, C, and d, [S] 1 (mM) [S] No inhibitor + 3 uM polyoxin Vo 1 Vo (nmoles min- 1 ) Vo (nmoles min- 1 ) Vo 0.32 OAO 3.125 2.5 0.097 0.114 10.3 8.8 0.053 0.063 18.9 15.8 0.60 1.67 0.150 6.7 0.088 11.4 1.00 1.0 0.200 5.0 0.128 7.8 2.00 0.5 0.267 3.75 0.196 5.1 1 [S](lnM)
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- Q. 1 J continued ..... b) (6 points) Use information from the graph your drew for Q. 1, part a) to determine Km and V max of chitin synthase. Identify the relevant information you obtain from the graph and show your calculation. From graph, -l/Km N -0.95, so Km = 1.05
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Unformatted text preview: (-1 mM) l/Vo = 2.4, so V max = 0.42 nmoles min-l c) (8 points) Determine the k; for polyoxin. In your calculation, use information you obtain from the graph you drew for part a) and show your calculation and any equation(s) you use. Determine -l/ K' m (for polyoxin) from x-intercept on graph = -0.44 N From this, K'm = 2.3 mM Determine k j from fonnula such as K'm = Km (l + [I]/K j ), i.e. k j = [I]/(K'm/Km)~l So, k i = 3 x 1O-6 /(2.3/l.05)-1 = 3 x 10-6 /1.19 = 2.5 ~.M d) (6 points) The substrate for chitin synthase is uridine diphosphate N-acetylglucosamine, whose structure is shown on the right. Which of structures A-E below is most likely to be that of polyoxin? Briefly explain your choice. c Polyoxin is a competitive inhibitor, and would therefore be expected to resemble the substrate UDPGlcNAc, which structure C does most closely....
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