Each enzyme is highly specific with regard to the type of chemical reaction that it catalyzes, and to the substances (called substrates) upon which it acts. This specific catalytic activity and its control by other biochemical constituents are of primary importance in the physiological functions of all organisms. Although all enzymes are proteins, they may, and usually do, contain additional nonprotein components called coenzymes that are essential for catalytic activity.

APOENZYME,  CATALYST,  COENZYME,  HOLOENZYME,  SUBSTRATE (CHEMICAL),  PROTEIN,  HORMONE,  EXTREMOZYMES,  TURNOVER NUMBER,  CELL