how to calculate Kcat value of enzyme

Analia Alet via (by analia_alet from
Mon Jan 21 09:35:46 EST 2008

 Hi, kcat = Vmax/Km, where Vmax could be expressed in mnol/(mg min) and Km in 
uM, so kcat is expressed in min-1

one good book explaining all this is

Enzyme Kinetics: Behavior and Analysis of Rapid Equilibrium and Steady-State 
Enzyme Systems (Wiley Classics Library)by Irwin H. Segel (Author) 

Best Regards

Good evening
> molecular weight of enzyme is 60 kDa and I took 4 ug of it in each
> reaction. Vmax and km values were obtained as 1.24 mmole/min/mg
> protein and mM. so how could i calculate Kcat value of the enzyme ?
> I will be very grateful for your kind cooperation.

 From your data you can first calcualte the molar amount of enzyme per  
reaction. Then re-express the velocity as mmole/min/mmole = 1/min, convert  
min to sec and you have the turnover number in 1/s = kat. If you have  
problems with any of that, ask your instructor to go through the  
calculation with you.

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