Multiple Choice
To calculate the turnover number of an enzyme, you need to know:
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6. Enzymes and Enzyme Kinetics
Kcat
Multiple Choice
If 10 μg of an enzyme (MW = 50,000 g/mol) is added to a solution containing a [substrate] 100 times greater than the Km, it catalyzes the conversion of 75 μmol of substrate into product in 3 min. What is the enzyme's turnover #?
A
1.25 x 105min-1
B
2.5 x 104min-1
C
1.5 x 102min-1
D
3.5 x 106min-1
Verified step by step guidance1
First, understand that the turnover number (kcat) is defined as the number of substrate molecules converted to product per enzyme molecule per unit time when the enzyme is fully saturated with substrate.
Calculate the number of moles of enzyme present. Use the formula: moles of enzyme = mass of enzyme (g) / molecular weight (g/mol). Convert 10 μg to grams (10 x 10^-6 g) and divide by the molecular weight (50,000 g/mol).
Determine the rate of reaction in terms of moles of substrate converted per minute. Given that 75 μmol of substrate is converted in 3 minutes, calculate the rate as 75 μmol / 3 min.
Convert the rate from μmol/min to mol/min by dividing by 10^6.
Finally, calculate the turnover number (kcat) using the formula: kcat = (rate of reaction in mol/min) / (moles of enzyme). This will give you the turnover number in min^-1.
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