calculate Kcat from Vmax

Dr Engelbert Buxbaum via (by engelbert_buxbaum from
Fri Sep 28 14:38:41 EST 2007

Am 27.09.2007, 06:09 Uhr, schrieb pp_fon <pesutcha from>:

> i wonder how to calculate a kcat from Vmax cause i get the Vmax value by  
> use a Michalis-Menten plot and the Unit of Vmax value is
> umol/min/mg(enzyme). and i use 0.0004 mg of enzyme per reaction and the  
> MW of enzyme is 64 kDa. How can i calculate the Vmax value

Vmax you get from non-linear curve fitting of your v vs [S] data to the  
Henri-Michaelis-Menten equation v = Vmax * [S] / (Km + [S]). Note that  
using linearisation (Lineweaver-Burk or the like) causes a lot of  
statistical problems, which in the days of supercomputer power on every  
desk we no longer need to accept. The unit of the velocity is mol/s = kat.

Since Vmax / [E] = kcat you need to calculate the molar concentration of  
enzyme (from molecular weight and the weight/volume concentration) and  
divide your Vmax by it. The result will have the unit of a 1st order rate  
constant, 1/s.

By the way, thou shallst not send messages to both the newsgroup and the  
private email address of its members.

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