Question

Determine the value of the turnover number of the enzyme invertase, given that Rmax (Vmax) for invertase = 15.8 mmol·L–1·min–1 and [E]t = 5.0 μmol·L–1. Invertase has a single active site.

__________ min ^-1

Answer 1

The turnover number (also termed k_cat) is defined as the maximum number of chemical conversions of substrate molecules per second that a single catalytic site will execute for a given enzymeconcentration . It can be calculated from the maximum reaction rate and catalyst site concentration as follows:

Before calculating, let's make sure we use the same units in both parameters:

Vmax = 15.8 mmol/(L min) = 15800 umol/(L min)

[E]t = 5.0 umol/L

Then,

Kcat = 15800/5 = 3160 min-1