Factors affecting enzyme action

Enzymes do not work at a fixed speed — turn a few dials and the rate rises, plateaus or crashes. In this lesson we investigate and explain the five factors that change the rate of an enzyme-catalysed reaction: temperature, pH (controlled with buffer solutions), enzyme concentration, substrate concentration and inhibitor concentration. We draw the temperature and pH curves and explain the optimum and denaturation, and we draw the substrate-concentration curve to reveal the maximum rate, Vmax. From Vmax we derive the Michaelis-Menten constant, Km, and use it to compare how strongly different enzymes hold their substrates — remembering that a low Km means a high affinity. We compare reversible inhibitors — competitive ones that fight for the active site and are beaten by more substrate, and non-competitive ones that bind an allosteric site and are not. Finally we immobilise an enzyme in alginate beads and weigh its slightly slower rate against being reusable and more stable.