[p8ragon]

hi everyone,

I'm learning biochemistry, and have recently started on concepts regarding K_cat. I'm stuck on what SHOULD be a relatively simple problem, and can't for the life of me figure it out :S

Enzyme Y, a homodimeric enzyme (35,000 Daltons) has a Vmax = 10 mM
of Product B/sec., when determined using a constant amount (500 μg) of
the enzyme in several enzyme assays (volume = 1 mL).
Each subunit has its own active site.
What is the value of kcat for this enzyme?


From my understanding, K_cat=Vmax/E

We are given Vmax and E, so it's a simple matter of converting them to M and G, respectively

Since the enzyme is homodimeric, and each kcat calculation is for a single active site, shouldn't we multiply it by 2?

The answer provided is 3.5x10^2 sec^-1... and i can't figure out why!

Thanks

[p8ragon]

Wow I'm an idiot. I just realized that the Enzyme units given were in Grams, and that I neded to convert them to mols for use in the kcat formula

but regardless, why would we divide the kcat value by 2 instead of multiplying it by 2? Is it because the K_cat value assumes that there is only one active site per enzyme, and since the # of active sites has doubled we have to divide it?

[Babcock_Hall]

Is 35,000 the molecular weight of the dimer, or is it the molecular weight of each monomer?