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Answer
(a) Calculate the reciprocal values for the data, as in parentheses below, and prepare a
double-reciprocal plot to determine the kinetic parameters.
Chapter 6 Enzymes S-69
V0 with 10 mg/mL ibuprofen
V0 (mM/min) (mM/min)
[S] (mM) (1/[S] (mM�1)) (1/V0 (min/mM)) (1/V0 (min/mM))
0.5 (2.0) 23.5 (0.043) 16.67 (0.0600)
1.0 (1.0) 32.2 (0.031) 25.25 (0.0396)
1.5 (0.67) 36.9 (0.027) 30.49 (0.0328)
2.5 (0.40) 41.8 (0.024) 37.04 (0.0270)
3.5 (0.28) 44.0 (0.023) 38.91 (0.0257)
The intercept on the vertical axis � �1/Vmax and the intercept on the horizontal 
axis � �1/Km. From these values, we can calculate Vmax and Km.
�1/Vmax � �0.0194, and Vmax � 51.5 mM/min
�1/Km � �1.7, and Km � 0.59 mM
(b) Ibuprofen acts as a competitive inhibitor. The double-reciprocal plot (with inhibitor)
shows that, in the presence of ibuprofen, the Vmax of the reaction is unchanged (the in-
tercept on the 1/V0 axis is the same) and Km is increased (�1/Km is closer to the origin).
13. Graphical Analysis of Vmax and Km The following experimental data were collected during a study
of the catalytic activity of an intestinal peptidase with the substrate glycylglycine:
Glycylglycine � H2O 88n 2 glycine
3210�1�2
0.02
0.04
0.06
0.08
0.10
1/
V
0
with inhibitor
1/[S]
Product formed Product formed
[S] (mM) (mmol/min) [S] (mM) (mmol/min)
1.5 0.21 4.0 0.33
2.0 0.24 8.0 0.40
3.0 0.28 16.0 0.45
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