Specificity constant

In the field of biochemistry, the specificity constant (also called kinetic efficiency or ${\displaystyle k_{cat}/K_{M}}$), is a measure of how efficiently an enzyme converts substrates into products. A comparison of specificity constants can also be used as a measure of the preference of an enzyme for different substrates (i.e., substrate specificity). The higher the specificity constant, the more the enzyme "prefers" that substrate.

The following equation, known as the Michaelis–Menten model, is used to describe the kinetics of enzymes:

where E, S, ES, and P represent enzyme, substrate, enzyme–substrate complex, and product, respectively. The symbols ${\displaystyle k_{f}}$, ${\displaystyle k_{r}}$, and ${\displaystyle k_{\mathrm {cat} }}$ denote the rate constants for the "forward" binding and "reverse" unbinding of substrate, and for the "catalytic" conversion of substrate into product, respectively.

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