This may be achieved by repressing or inducing its synthesis, or controlling the amounts of other enzymes which degrade it. However the activity of individual enzyme molecules may be reduced by inhibitors or increased by effectors . An enzyme molecule will be inactivated if the substrate can no longer bind to the active site. This may be effected by an inhibitor covalently bonding to the site, or binding very tightly so that its dissociation is very slow. In reversible inhibition , there is a rapid equilibrium of the enzyme and inhibitor.
Competitive inhibitors bind to the active site.
Effector molecules may act by having an opposite effect. Examine the pdb file with RasMol. Coenzymes Many enzymes require coenzymes in order to function. Coenzymes are bound at the active site in order to interact with the substrate and play an essential role in the catalysed reaction. They act as carriers of a variety of chemical groups.