Enzymes are generally divided into simple enzymes and bound enzymes, not all of which are proteins. However, most of them are proteins, such as simple proteases, which are composed mainly of proteins. Enzymes made up of bound proteins are formed by combining protein components and non-protein components. Only this kind of enzyme that combines both substances can be biologically active and is a bound enzyme, also called a whole enzyme. Enzymes composed of proteins alone are mainly composed of proteins.