The turnover number for an enzyme is equivalent to the number of substrate molecules processed per second per enzyme molecule. To a test tube containing a 100 mM concentration of its substrate, you have added an enzyme at a final concentration of 10 µM, and have measured the rate of the reaction to be approximately 500 µM/sec. If the Km for the binding of the enzyme to this substrate is about 100 mM, what is the turnover number?
A) 100
B) 500
C) 1000
D) 5000
E) 10,000

Question

Quizplus · Accepted Answer

Under these conditions, we have: [S] = K_m = 100 mM. This means the rate of reaction is: V = ½ × V_max. Thus, V_max = 2 × 500 µM/sec = 1000 µM/sec. Finally, turnover number is equal to this rate divided by the enzyme concentration; that is: k_cat = (1000 µM/sec) / (10 µM) = 100 per second.

The Turnover Number for an Enzyme Is Equivalent to the Number