Factors affecting enzyme activity

Conditions that alter a protein's tertiary structure change enzyme activity: temperature, pH, substrate concentration, and the binding of specific chemicals that regulate it.

Enzymes work within a narrow range of temperature and pH. Each shows its highest activity at an optimum temperature and an optimum pH, and activity falls on either side of the optimum.

Low temperature keeps an enzyme temporarily inactive, while high temperature destroys its activity because heat denatures proteins.

As substrate concentration rises, reaction velocity rises at first and then levels off at a maximum velocity (Vmax) that more substrate cannot exceed. There are fewer enzyme molecules than substrate molecules, and once all are occupied no free enzyme is left for the extra substrate.

When a chemical that binds to the enzyme shuts off its activity, the process is inhibition and the chemical is an inhibitor.

A competitive inhibitor closely resembles the substrate and competes with it for the substrate-binding site, so the substrate cannot bind and activity falls. Malonate inhibits succinic dehydrogenase because it closely resembles the substrate, succinate.

Competitive inhibitors are often used to control bacterial pathogens.