The catalytic constant (kcat) or turnover number is the number of enzymatic reactions a single saturated enzyme molecule can catalyze per unit of time, usually expressed in s-1. kcat is not dependent on the concentration of the enzyme, and is, therefore, a better parameter than Vmax for comparing different enzymes. Because kcat is the maximum number of chemical reactions a single enzyme molecule can catalyze, the maximum velocity (Vmax) at a specific enzyme concentration is obtained by multiplying kcat with the concentration of the enzyme ([E]), i.e., Vmax = kcat • [E]. This means, that if Vmax and [E], which can be experimentally measured, are known, kcat can be calculated as follows [1].

kcat = Vmax/[E]


  1. Lehninger, Albert L.; Nelson, David L.; Cox, Michael M. (2008). Principles of Biochemistry (5th ed.). New York, NY: W.H. Freeman and Company. ISBN 978-0-7167-7108-1.


Theory overview