Proteins are the agents of biological function. Virtually every cellular activity is dependent on one or more particular proteins. Thus, a convenient way to classify the enormous number of proteins is by the biological roles they fill. By far the largest class of proteins is enzyme. A number of proteins do not perform any obvious chemical transformation but nevertheless regulate the ability of other proteins to carry out their physiological functions. Such proteins are referred to as regulatory proteins. Transport proteins, storage proteins and structural proteins are proteins carry out respective functions.