Question

What is the unit of catalytic efficiency kcat/Km?

(a) conc^-1 time^-1

(b) conc time

(c) conc^-2time^-2

(d) conc time-1

The question was asked in a national level competition.

This interesting question is from Determining Enzyme Kinetic Constants from Batch Data in division Homogenous Reactions of Bioprocess Engineering

Answer 1

The correct choice is (a) conc^-1 time^-1

For explanation I would say: When calculating Kcat, the concentration units cancel out, so Kcat is expressed in units of inverse time. It is the turnover number – the number of substrate molecule each enzyme site converts to product per unit time. The units of Km are those of concentration i.e. mM, mM or Km is the concentration of substrate at which half maximal velocity is observed.