Dan Price, age 13, of Chilliwack, B.C., Canada, for his question:

What is meant by enzymes?

The word enzyme is related to leavening, which gives a clue to its meaning. Enzymes are complex chemicals that act like the yeast that triggers the sugar in bread dough to change itself into alcohol and spongy bubbles of carbon dioxide gas. This is a fermenting or leavening process    governed by special enzymes in the yeast cells. These and other enzymes are classed as catalysts. This is because they remain unchanged by the various chemical reactions which they trigger, speed up or sometimes govern.

Enzymes are highly complex proteins and each participates in a certain highly complex biochemical function. They are essential to all plant and animal life. Some are needed by decay bacteria, others are needed to make cheese, bread and other processed foods. The most interesting enzymes to us are those that perform their miracles in the human body. At present, we know of more than 700 of them, all essential to good health. They are present in infinitesimal quantities, which makes identification difficult. No doubt more will be discovered and certainly medical science needs to know much more about the intricate roles they play.

The first enzyme was discovered way back in 1833. It is a diastase, which speeds up the conversion of starch into sugar. We now know that a team of different enzymes works to govern the many digestive operations to break foods into simpler nutrients that can be absorbed by the body. Pepsin, for example, works with the stomach's strong hydrochloric acid to break down proteins into usable amino acids.

The B complex vitamins contain a variety of enzymes essential to the miraculous operations of metabolism. Some enzymes are vital to the mitochondria, those dynamic little powerhouses that produce cellular energy. Others trigger various hormones to perform their functions. Certain enzymes in the body's fluids play key roles in building and repairing tissues and in the complex operation that causes the blood to clot.

Researchers are busy investigating some very subtle enzymes that govern certain operations in the cell nucleus. These work with DNA, the blueprint chemical that governs all cellular activity. Linkages have been traced between certain enzymes and the hereditary genes. At present, medical researchers know enough about enzymes to fill a library    but they feel that their investigations have barely begun

It is true that an enzyme is not changed by the chemical operation it triggers. But enzymes are not indestructible. Many are destroyed by certain strong chemicals or by heat. After suffering a high temperature, a patient may be left with an enzyme deficiency. The usefulness of some enzymes may be inhibited by other chemicals in the body. Certainly all these enzymes present a most intricate challenge. If such research enchants you, it is nice to know that the fabulous work ahead is almost unlimited.