Multiple Choice
To calculate the turnover number of an enzyme, you need to know:
6. Enzymes and Enzyme Kinetics
Kcat
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The turnover number for an enzyme is known to be 5000 min-1. From the following set of data, determine both the Km and the total amount of enzyme ET.
A) What is the Km of the enzyme?
a) 1 mM.
b) 2 mM.
c) 4 mM.
d) 1000 mM.
B) What is the total amount of enzyme?
A
0.001 μM.
B
0.01 μM.
C
0.1 μM.
D
10 μM.
Verified step by step guidance1
To determine the Km, we need to analyze the data using the Michaelis-Menten equation: v = (Vmax * [S]) / (Km + [S]). Here, v is the initial velocity, [S] is the substrate concentration, Vmax is the maximum velocity, and Km is the Michaelis constant.
From the data, observe that the initial velocity approaches a maximum value (Vmax) as the substrate concentration increases. The Vmax can be estimated from the highest velocities, which are 498 and 499 μmol/min.
To find Km, identify the substrate concentration at which the initial velocity is half of Vmax. This is the substrate concentration where v = Vmax/2. From the data, estimate Vmax/2 and find the corresponding [S].
For the total enzyme concentration (ET), use the relationship Vmax = kcat * [ET], where kcat is the turnover number. Given kcat = 5000 min⁻¹, rearrange the equation to solve for [ET]: [ET] = Vmax / kcat.
Substitute the estimated Vmax and given kcat into the equation to calculate the total enzyme concentration [ET].
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