Although graphical methods are employed for accurate determination of the V max
ID: 843314 • Letter: A
Question
Although graphical methods are employed for accurate determination of the Vmax and Km of an enzyme-catalyzed reaction, sometimes these quantities can be quickly estimated by inspecting values of the initial rates, v, at increasing [S]. Estimate the Vmax and Km values of the enzyme-catalyzed reaction for the following data shown in the columns below:
[S] (M)
v0, (moles/min/)
2.5 x 10-6
28
4.0 x 10-6
40
1 x10-5
70
2 x 10-5
95
4 x 10-5
112
1 x 10 -4
128
2 x 10-3
139
1 x 10-2
140
[S] (M)
v0, (moles/min/)
2.5 x 10-6
28
4.0 x 10-6
40
1 x10-5
70
2 x 10-5
95
4 x 10-5
112
1 x 10 -4
128
2 x 10-3
139
1 x 10-2
140
Explanation / Answer
Notice how little the velocity changes as the substrate concentration increases by fivefold from 2 to 10 ?M. Thus, we can estimate a Vmax of 140 ?M/min. Km is defined as the substrate concentration that produces a velocity of (1/2 Vmax), or 70 ?M/min. Inspection of the table indicates that this V0 occurs at [S] 1*10^-5 M, thus Km ? 1 *10^-5 M
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