Enzymes and Protein Drugs

ENZYMES

Enzymes are organic catalysts produced in the body by living organisms. They perform many complex chemical reactions that make up life processes. Enzymes are lifeless and when isolated, they still exert their characteristic catalytic effect. Their chemical composition varies, and they do show several common properties. They are colloids, soluble in water and dilute alcohol but are precipitated by concentrated alcohol. Most enzymes act best at temperatures between 35 and 40°C; temperatures above 65°C, especially in the presence of moisture, destroy them, whereas their activity is negligible at 0°C. Certain heavy metals, formaldehyde, and free iodine retard the enzymes activity. Their activity is markedly affected by the pH of the medium in which they act or by the presence of other substances in this medium. They are highly selective in their action.

The enzymes are proteins having molecular weight from about 13,000 to 8,40,000. At present they are divided according to their action by a complex system established by the Commission on Enzymes of the International Union of Biochemistry. Six major classes are recognized; each has 4 to 13 subclasses, and each enzyme is assigned a systematic code number (B.C.) composed of 4 digits. The major classes are given in table below.

Enzymes are found in combination with inorganic or organic substances that have an important part in the catalytic action. If these are nonprotein organic compounds, they are known as coenzymes. If they are inorganic ions, they are referred to as activators. Coenzymes are integral components of a large number of enzyme systems. Several vitamins (thiamine, riboflavin, nicotinic acid) have a coenzymatic function.

Enzymes are obtained from plant and animal cells and many have been purified. They are used as therapeutic agents and as controlling factors in certain chemical reactions in industry. Pepsin, pancreatin, and papain are used therapeutically as digestants. Hyaluronidase facilitates the diffusion of injected fluids. Streptokinase and streptodornase dissolve clotted blood and purulent accumulations. Zymase and rennin are used in the fermentation and cheese industries; and penicillinase inactivates the various penicillins.

Table : International classification of enzymes

The names used to designate enzymes usually end in -ase or -in. The important enzymes are given hereunder.

Properties of Enzymes

1.     Enzymes are sensitive to heat and are denatured by excess heat or cold, i.e. their active site becomes permanently warped, thus the enzyme is unable to form an enzyme substrate complex. This is what happens when you fry an egg, the egg white (augmentin, a type of protein, not an enzyme), is denatured.

2.     Enzymes are created in cells but are capable of functioning out side of the cell. This allows the enzymes to be immobilized, without killing them.

3.     Enzymes are sensitive to pH, the rate at which they can conduct reaction is dependent upon the pH of where the reaction is taking place, for example, pepsin in the stomach has an optimum pH of about 2, whereas salivary amylase has an optimum pH of about 7.

4.     Enzymes are reusable and some enzymes are capable of catalysing many hundreds of thousands of reactions, for example, catalase working on hydrogen peroxide, try putting some liver into hydrogen peroxide.

5.     Enzymes will only catalyse one reaction, for example, invertase will only produce glucose and fructose, when a glucose solution is passed over beads of enzyme.

6.     Enzymes are capable of working in reverse, this act as a cut off point for the amount of product being produced. If there are excess reactants, the reaction will keep going and be reversed, so that there is no overload or build up of product.