Upon binding substrates the enzyme changes shape such that bonds in the reactants are stressed and are therefore more easily broken, and the substrates are oriented such that formation of new bonds is favored. Once the product forms it is released and the enzyme returns to its initial state. Because of the precise relationship between the enzyme and its substrate, each enzyme can only catalyze a narrow range of reactions. Once the products become free from the enzyme, the enzyme can catalyze another reaction. Because enzymes can catalyze multiple reactions a small amount of enzyme can cause a dramatic increase in the reaction rate.
Various factors influence the effectiveness of an enzyme.
Therefore, factors such as salt concentration, pH, temperature, and organic solvents have a major effect on enzyme activity. A second set of factors, since enzymes catalyze chemical reactions, are those which influence any chemical reaction, such as substrate concentration and temperature. Finally, since enzymes must bind substrates to catalyze the reaction, and each reaction requires a certain amount of time, the enzyme concentration also influences the reaction rate. Because enzymes act to increase reaction rates we can measure how well an enzyme is working by measuring its kinetics, that is, the rate of the reaction that it catalyzes. This is often conveniently done by measuring the rate at which the products accumulate.