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Why is Vmax not a constant? Why do we want to analyze kcat instead of Vmax?

Why is Vmax not a constant? Why do we want to analyze kcat instead of Vmax?

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Expert Solution

Vmax not a constant
Vmax is dependent on the enzyme concentration and substrate concentration, which changes during the time course.

but Kcat is constant
kcat is independent of any concentration and so is a constant.

Chemical kinetics in general states that the reaction rate depends on the concentrations of the reactants. Although enzymes are catalysts, Vmax does depend on the enzyme concentration, because it is just a rate, mol/sec - more enzyme will convert more substrate moles into product. In standard Michealis-Menten kinetics the reaction constant is proportional to the rate of the decomposition of ES (enzyme-substrate complexes). If you want to be exact, never use Vmax in your reports, always find out the concentration of active enzyme (or assume that all enzyme is active) and devide Vmax by [E] (enzyme concentration), obtain Kcat that way, which is reciprocal sec, independent of anything.

queen_honey_blossom answered 2 years ago
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