= Inhibition constant
{title2=$K_i$, $K_i'$}
An <inhibition constant> sets an inhibitor <concentration> scale in an <enzyme kinetics> model. In the rapid-binding construction under <reversible enzyme inhibition>, $K_i=[E]I/[EI]$ and $K_i'=[ES]I/[ESI]$ are <dissociation constants>. Smaller values favour the corresponding bound population at fixed free inhibitor <concentration>. More generally, fitted <inhibition constants> need not be true binding <dissociation constants>; a mechanism must justify that interpretation.<Symbolism and Terminology in Enzyme Kinetics (Recommendation 1981) by Nomenclature Committee of the International Union of Biochemistry>[Symbolism and Terminology in Enzyme Kinetics, section 6.4, final paragraphs: operational inhibition constants versus explicitly defined dissociation constants]{ref}
For example, choosing $I=K_i$ makes $[EI]=[E]$ in this model, but does not imply that half of all <enzyme> is $EI$: $ES$ and $ESI$ also contribute to the total population.
Back to article page
