CHEM344 HW#4 Due: Fri, Feb 21@2pm BEFORE CLASS! HW to be handed in: Atkins(9th ed.) Chapter 23: Exercises: 23.2(b), 23.4(b) Problems: 23.1, 23.4 Tinoco (4th ed.) Chapter 8: 3, 5, 11, 20 Extra (do not hand in): Tinoco (4th ed.) Chapter 8: 1, 14, 18, 19 1. [23.2(b)] The enzyme-catalysed conversion of a substrate at 25°C has a Michaelis constant of 0.032 mol dm−3. The rate of the reaction is 2.05 × 10−4 mol dm−3 s−1 when the substrate concentration is 0.875 mol dm−3. What is the maximum velocity of this reaction? 2. [23.4(b)] Consider an enzyme-catalysed reaction that follows Michaelis–Menten kinetics with KM = 7.5 × 10−4 mol dm−3. What concentration of a competitive inhibitor characterized by KI = 5.6 × 10−4 mol dm−3 will reduce the rate of formation of product by 75 per cent when the substrate concentration is held at 1.0 × 10−4 mol dm−3? 3. [23.1] The following results were obtained for the action of an ATPase on ATP at 20°C, when the concentration of the ATPase was 20 nmol dm−3: [ATP]/(μmol dm−3) 0.60 0.80 1.4 2.0 3.0 v/(μmol dm−3 s−1) 0.81 0.97 1.30 1.47 1.69 Determine the Michaelis constant, the maximum velocity of the reaction, the turnover number, and the catalytic efficiency of the enzyme. 4. [23.4] The enzyme carboxypeptidase catalyses the hydrolysis of polypeptides and here we consider its inhibition. The following results were obtained when the rate of the enzymolysis of carbobenzoxy-glycyl-d-phenylalanine (CBGP) was monitored without inhibitor: [CBGP]0/(10−2 mol dm−3) 1.25 3.84 5.81 7.13 Relative reaction rate 0.398 0.669 0.859 1.000 (All rates in this problem were measured with the same concentration of enzyme and are relative to the rate measured when [CBGP]0 = 0.0713 mol dm−3 in the absence of inhibitor.) When 2.0 × 10−3 mol dm−3 phenylbutyrate ion was added to a solution containing the enzyme and substrate, the following results were obtained: [CBGP]0/(10−2 mol dm−3) 1.25 2.50 4.00 5.50 Relative reaction rate 0.172 0.301 0.344 0.548 In a separate experiment, the effect of 5.0 × 10−2 mol dm−3 benzoate ion was monitored and the results were: [CBGP]0/(10−2 mol dm−3) 1.75 2.50 5.00 10.00 Relative reaction rate 0.183 0.201 0.231 0.246 Determine the mode of inhibition of carboxypeptidase by the phenylbutyrate ion and benzoate ion.

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