Man's physical universe

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VITAMINS, ENZYMES, AND HORMONES 743

in the growth of bread mold, while one trillionth of a grain of vitamin

H (biotin) produces a measurable effect on another mold.

There are at least a dozen vitamin-like substances that affect plants.

The action of vitamins on plants seems to resemble their action on

animals in that they serve as coenzymes. Coenzymes are substances

which are essential to the action of enzymes; for example, vitamin Bi

(thiamin) combines with phosphates to form an enzyme which catalyzes

the breakdown of pyruvic acid, one of the products of the catabolism

of carbohydrates.

Enzymes Catalyze the Digestion of Foods by Living Organisms.

Living organisms of all kinds, ranging from bacteria, yeasts, and

molds to plants and animals, produce enzymes whose main function

is to catalyze the splitting of such foods as carbohydrates, fats, and

proteins into smaller molecules. This process is called digestion.

Enzymes are not living organisms because they cannot reproduce

themselves, but they do behave like living organisms in that they are

inactivated by heat and various poisons.

There Are Two Main Classes of Enzjrmes.

Many enzymes catalyze the reaction of foods with oxygen; other

enzymes specialize in the hydrolysis of proteins, fats, and carbohydrates.

The oxidative enzymes frequently make a nuisance of

themselves, oxidizing vitamins and causing the spoilage of foods in

storage; the hydrolytic enzymes on the other hand are utilized

considerably

in industry for the production of amino acids and other

substances produced by the hydrolysis of proteins and other types of

organic compounds.

In the quick-freezing of foods, it has been found necessary to blanch

the foods, i.e., heat them for a short time in order to destroy the

oxidative enzymes which would otherwise oxidize some of the vitamins

in the foods even while they are kept below the freezing-point.

Ascorbase

is an enzyme that catalyzes the oxidation of ascorbic acid, while

peroxidase catalyzes the oxidation of such fruits as peaches, bananas,

and apples, causing them to turn brown in a short time after exposure

to the atmosphere. Sulfur dioxide is used to inactivate these enzymes

in the drying of fruits in order to keep them from darkening in color.

Pineapple juice and grapefruit juice are also effective in

inactivating

these oxidative enzymes.

The digestion of foods in the human body is accomplished by

enzymes shown in the following table:

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