1. What is the advantage of using a substrate concentration near the K m in I 50
ID: 1026891 • Letter: 1
Question
1. What is the advantage of using a substrate concentration near the Km in I50 determinations?
2. Estimate the I50 from the data below. How did you come to this conclusion?
[I] (mM) Activity (A/minute)
0 0.53
3.75 0.38
7.5 0.29
15 0.19
30 0.11
60 0.05
120 0.02
3. The data in the table below were obtained by performing Km determination experiments in the absence of inhibitor and in the presence of two different inhibitors.
a. What type of inhibitor is Inhibitor 1? Why?
b. What type of inhibitor is Inhibitor 2? Why?
c. What are the Ki values for Inhibitor 1 and Inhibitor 2?
Velocity (µmol/min)
Substrate (mM)
No Inhibitor
Inhibitor 1
(1 mM)
Inhibitor 2
(1 mM)
0.25
0.06
0.02
0.02
0.5
0.10
0.05
0.04
1
0.17
0.08
0.07
2
0.25
0.14
0.10
4
0.33
0.22
0.13
8
0.40
0.31
0.16
Velocity (µmol/min)
Substrate (mM)
No Inhibitor
Inhibitor 1
(1 mM)
Inhibitor 2
(1 mM)
0.25
0.06
0.02
0.02
0.5
0.10
0.05
0.04
1
0.17
0.08
0.07
2
0.25
0.14
0.10
4
0.33
0.22
0.13
8
0.40
0.31
0.16
Explanation / Answer
Ans 1: At substrate concentration near Km, the enzyme shows significant catalysis and yet is susceptible to changes in the substrate concentration. This is the biochemical advantage of having a substrate concentrations near the Km value. In order to study which inhibitor is more effective, we need to understand the rate at which the enzyme reacts. And the plot between the concentration and the activity gives the performance of the inhibitor. The I50 is the concentration of the inhibitor required to reduce the rate of the enzymatic reaction by 50%.
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