3.2.4. Inhibition of Enzyme Reactions

Types of Inhibition. The function of enzyme-based biosensors may be severely restricted by inhibitors. The inhibition is either reversible or results in an irre-versible inactivation of the enzyme.

Competitive Inhibition. Inhibitors structurally related to the substrate may be bound to the enzyme active center and compete with the substrate (competitive inhibition).

Non-competitive Inhibition. If the inhibitor is not only bound to the enzyme but also to the enzyme-substrate complex, the active center is usually deformed and its function is thus impaired; in this case the substrate and the inhibitor do not compete with each other (noncompetitive inhibition). Competitive and noncompetitive inhibition effect the enzyme kinetics differently. A competitive inhibitor does not change Vmax but increases KM (Fig. 3.9a) in contrast, noncompetitive inhibition results in an unchanged KM and an increased Vmax (Fig. 3.9b). Some enzymes, e.g. invertase, are inhibited by high product concentration (product inhibition).