Question

An enzyme is found that catalyzes the reaction A ↔B. In an experiment with total enzyme concentration of 5 nM, Vmax is 1.5 μM s^-1. What is kcat for the enzyme. Give your answer as a number only in units of s^-1.

Answer 1

Ans. Kcat is the number of molecules of product (here B in given reaction) formed in a enzyme catalysed reaction in unit time or per second.

The formula to calculate Kcat is as following:

Kcat = Vmax / Total Enzyme concentration. Unit = molecules/ second or molecules s^-1.

Where Vmax is the maximum reaction rate when all enzymes are saturated by substrates.

Putting all given values ( convert enzyme conc. in μM as it is given in nM; same scale):

Kcat = 1.5 μM s^-1 / 5x10^-3 μM

= 300 s^-1 .