Enzymes are present in all living creatures: animals, plants, algae, fungi, and bacteria. They regulate the complex chemical reactions of life. Enzymes are catalysts: that is, they take part in chemical reactions without themselves being permanently changed by the reaction. Thus one molecule of an enzyme can work successively on many molecules of other substances, so enzymes are effective in tiny amounts. And effective they are: the artificial catalysts used in industry usually need high pressures and temperatures to work, but enyzmes operate quite happily at ambient pressure and body temperature.
