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
−2
−3
In a separate experiment, the effect of 5.0 × 10 mol dm 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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8.
EXTRA: DO NOT HAND IN
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