An enzyme catalyzes the reaction A ® B. The initial rate of the reaction was mea
ID: 895636 • Letter: A
Question
An enzyme catalyzes the reaction A ® B. The initial rate of the reaction was measured as a function of the concentration of A. The following data were obtained:
[A], M V0, moles/min
0.05 0.08
0.1 0.16
0.5 0.79
1 1.6
5 7.3
10 13
50 40
100 53
500 73
1,000 76
5,000 79
10,000 80
20,000 80
By simply observing the data table, estimate the Vmax for the enzyme with substrate A?
What is the Km of enzyme for substrate A?
Calculate the value of V0 when [A] = 43?
The above data was plotted as 1/ V0 vs. 1/[A], and a straight line was obtained.
What is the value of the y-intercept of the line?
What is the value of the x-intercept of the line?
Explanation / Answer
Clearly from the data vmax = 80 moles/min, because it remains same when [A] is changed from 10,000 M to 20,000 M.
Now
v0 = vmax / 1 + KM/[A]
Now when [A] = 50 M, v0 = 40 moles/min
or 40 moles/min = (80 moles/min)/ 1 + KM/(1 M)
or KM = 50 M
when [A] = 43 M, v0 = 80/ 1+ (50/43) = 37 moles/min
y-intercept of the line = 1/ vmax
x-intercept of the line = - 1/ KM