conversion of rate to kcat?

Dr Engelbert Buxbaum engelbert_buxbaum at
Mon Mar 20 04:15:53 EST 2006

j.nilsson at wrote:

> Hi!
> How would I go about converting the rate of an enzyme (nmol / min) to
> kcat?
> (Mr of enzyme is 125000 and a 0.01 ml sample was assayed(if this info
> helps..?)
> Im a little new to this subject thats why im asking this question...

No, the data you gave are insufficient.

kcat = Vmax / [E]

So assuming that your conversion rate is in fact Vmax and not only V at
some arbitrary [S], you need the molar concentration of the enzyme. This
you can calculate from the molecular weight if the enzyme concentration
(mg/ml or the like) is given, which you didn't supply. 

Oh, and when you do the calculation don't forget to convert all values
to basic units, so you get the order of magnitude right! Most errors
occur at this point.

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