Enzymes are a group of complex proteins or conjugated proteins that are produced by living cells and act as catalysts in specific biochemical reactions. Enzymes are natural proteins produced in minute quantities by all living organisms (bacteria, plants, and animals) and functioning as highly selective biochemical catalysts by converting one molecule into another.

Although enzymes are large protein molecules with hundreds of amino acids, only a small part of the enzyme participates in the catalysis of a biochemical reaction. This is called the active site. The three-dimensional structure of the enzyme determines the appearance of the active site. The active site precisely accommodates the shape of a biological substrate. The enzyme and substrate fit together like a key in a lock, and only substrates with the right shape will be transformed by an enzyme. This is what makes enzymes specific in their action. In addition to a substrate, the action of enzymes is dependent on time, enzyme concentration, temperature, pH levels and the presence of stabilizers or inhibitors.

Enzymes are essential to life because they speed up metabolic reactions to a very great extent, but do not undergo any change in themselves. In human beings, food that is ingested is not recognized by intestinal epithelium in its form and need to be converted into smaller molecules that are absorbed into the blood system. Enzymes found in human beings are secreted by glands, however industrial enzymes are produced via fermentation process.