when 10 micrograms of an enzyme (MW 50,000) is added to a reaction mixture containing its substrate at a concentration 100 times the km, it catalyzes the conversaion of 75 micromole of substrate into product in 3 mins. what is the enzyme turn over number (kcat)?
ive been trying to solve this problem for 30 mins i dont understand it.. i think v max is 25 micromol/min but i dont know what to do with the MW of the enzyme cause its in daltons i believe and i need that in moles... im so confused
1 Dalton is 1 amu is 1 g/mol. The turnover number is the number of rxns per second an enzyme molecule can catalyze (or, the number of moles of rxns that a mole of enzyme molecules can catalyze in a second). Vmax is the turnover number multiplied by the amount of enzyme you actually have in the pot (we'll see if your Vmax is right).
At 100 times Km you've saturated the enzyme sites, so every molecule of enzyme is catalyzing rxns as fast as it can go:
(75 umol substrate / 3 min) / (10 ug enzyme / 50000 g/mol)
= 125000 (mol substrate / mol enzyme) / min
x (1 min / 60 s) = 2083 /s
So you see, you could have calculated the turnover number from either the Vmax you were given, or from the amounts (or, alternatively, the concentrations) of enzyme and substrate that was catalyzed.
Except you panicked. AAAAAAAGGHHHH!
m
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