Enzymes are protein molecules made up of chains of amino acids. They play a very important role and work more capably than any reagent concocted by chemists. The specificity of an enzyme is related to the formation of the enzyme substrate complex which requires that the proper groupings of both substrate and enzyme should be in correct relative position. Enzymes which are used in the cells which make them are called intracellular enzymes. Enzymes which are produced in cells which secrete them to other parts of the body are known as extra cellular enzymes. Digestive juices are an instance of the latter type. There are few enzymes, whose names have been established by long usage such as ptyalin, pepsin, trypsin and erepsin. Apart from these, enzymes are generally named by adding the suffixes to the main part of the name of the substrate upon which they act. Thus amylases act upon starch (amylum), lactase acts upon lactose, lipases act upon lipids, maltase acts upon maltose and protesses act upon lipids, maltase acts upon maltose and protesses act upon proteins.
There are, nevertheless, quite a lot of enzymes which act upon many substances in different ways. These enzymes are named by their functions rather than substrates. Some enzymes work proficiently only if some other specific substance is present in addition to substrate. This other substance is known as an "activator" or a "conenzyme". Many of the conenzymes are related to vitamins. Conenzymes, like enzymes, are being incessantly regenerated in the cells. Enzymes play a crucial role in the digestion of food as they are responsible for the chemical changes which the food undergoes for the period of digestion. The chemical changes comprise the breaking up of the large molecules of carbohydrates, fats and proteins into smaller ones or conversion of complex substances into simple ones which can be absorbed by the intestines.
Enzymes also control the numerous reactions by which these simple substances are utilised in the body for building up new tissues and producing energy. The enzymes themselves are not broken down or changed in the process. They remain as powerful at the end of a reaction as they were at the beginning. Furthermore, very small amounts can convert large amounts of material. They are thus true catalysts. The process of digestion begins in the mouth. The saliva in the mouth, besides helping to masticate the food, carries an enzyme called ptyalin which begins the chemical action of digestion. It initiates the catabolism of carbohydrates by converting starches into simple sugars. This explains the need for systematic mastication of starchy food in the mouth. If this is not done the ptyalin cannot carry out its functions as it is active in an alkaline, neutral or slightly acid medium and is inactivated by the extremely acid gastric juices in the stomach. Even though enzymatic action starts while food is being chewed, digestion moves into high gear only when the chewed food has passed the esophagus and reached the stomach. The enzyme or active principle of the gastric juice is pepsin. This enzyme in combination with hydrochloric acid starts the breakdown of proteins into absorbable amino acids called polypeptides. An additional enzyme, rennin, plays an imperative role in the stomach of the infant.
The pancreas contributes various enzymes which carry on the breakdown of proteins, help to divide starch into sugars and work with bile in digesting fats. The small intestine itself secretes enzymes from its inner wall to complete the reactions. When all the enzymes have done their work, the food is digested and rendered fit for absorption by the system. Raw foods contain enzymes in abundance; pasteurising, pickling, cooking, smoking and other processing denature enzymes. It is, therefore, necessary to include in our diet, considerable amount of raw foods in the form of fruits, raw salads and sprouts. Studies have revealed that the body without sufficient raw materials from raw foods may exhaust and produce fewer enzymes year after year. This may lead to wearing out of body processes and consequent worn out looks.