Complex Enzyme-Substrate Interactions
Complex enzyme kinetics can arise when an enzyme has more than one substrate, or more than one product, or both, for the reaction it catalyzes. These situations represent the rule rather than the exception. Generally, in an experimental setting, enzyme reactions that involve more than one substrate are set up with all but one of the substrates at saturating concentration. Therefore, it is important to be able to recognize the effects of multiple substrates and/or multiple products on the kinetic behavior of enzymes. The enzyme and only one of the substrates, at several different concentrations, are combined and the amount of bound substrate is determined. There are several enzymes that have more than one catalytic site for the same substrate. Often these are enzymes with more than one subunit, where each subunit will have an active site. Cooperativity in enzyme kinetics follows the same general rules as cooperativity in ligand binding and receptor kinetics.