Catalytic efficiency

Catalytic efficiency is also called the specific constant.

Introduction:

An enzyme with a high Km requires a higher substrate concentration to achieve a given reaction velocity than an enzyme with a low Km for the same K_cat (catalytic constant or turnover number). At very low substrate concentrations, where [S] << K_m, most of the enzyme is free.

Thus, it is matter to think that [E]=[Et], where Et is the total concentration of enzyme. So that the Michaelis Menten equation becomes in another way, which is presented in the next segment.

The equation:

The description of the Catalytic efficiency:

Thus, the ratio K_cat/K_m is equivalent to the rate constant for the reaction between the free enzyme and the free substrate. K_cat/K_m is the ratio called specific constant is a measure of catalytic efficiency. It means how efficiently an enzyme converts substrate to product at low substrate concentration. It has units of M^-1s^-1.

Thus, the rate of product formation is dependent on both how well the enzyme binds substrate and how fast the enzyme converts the substrate into a product once the substrate is bound.

Note that, either a large value of K_cat (which means high turnover number of an enzyme) or a small value of Km (which means high affinity for the substrate) will make K_cat/K_m large.

A comparison of K_cat/K_m for the same enzyme with different substrates, or for two enzymes with with different substrates, is widely used as a measure of Catalytic efficiency.

Other related notes:

Enzyme inhibition: https://thebiologyislove.com/enzyme-inhibition/

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