Page 201 - Academic Press Encyclopedia of Physical Science and Technology 3rd BioChemistry

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Encyclopedia of Physical Science and Technology EN017G-116 August 2, 2001 18:14

Vitamins and Coenzymes

David E. Metzler
Iowa State University

I. The Discovery of Vitamins and Coenzymes
II. Nutritional Recommendations
III. Chemical Properties and Functions

GLOSSARY bacteria, protozoa, fungi, higher plants, animals, or hu-
man beings. Some vitamins are incorporated into the coen-
Coenzymes Small organic molecules that function to- zymes in which they function. Others become chemically
gether with enzymes to catalyze specific types of chem- attached to proteins and act as bound coenzymes, often
ical reactions. described as prosthetic groups. Vitamin C (ascorbic acid)
Growth factor A material needed in small amounts for functions as a coenzyme without any firm attachment to a
growth of an organism. Growth factors for animals are protein. Vitamin A, in one of its forms (retinoic acid), acts
vitamins but other substances may also be growth fac- as a hormone. Vitamin D, which can be formed in the skin
tors for bacteria, yeasts, etc. by the action of sunlight, is a natural precursor to oxygen-
Prosthetic groups Coenzymes or similar cocatalytic containing derivatives which also act as hormones. Most
groups that are firmly attached, usually by covalent modern human beings would have difficulty in meeting
linkages, to enzymes. the body’s needs for vitamin D by sunbathing; hence the
Vitamins Naturally occurring organic compounds that designation of this prohormone as vitamin D.
for human beings are essential nutrients in very small
amounts. Vitamins are often components of coenzymes
and prosthetic groups. I. THE DISCOVERY OF VITAMINS
AND COENZYMES

COENZYMES are small organic molecules that func- As early as 1750 it was recognized that green vegetables
tion with thousands of different enzymes in all organ- and citrus fruits could prevent the dread disease scurvy,
isms, assisting in the catalytic processes needed for life. whichafflictedancientseavoyagers,causinghemorrhages
They often contain vitamins as components. Several coen- of skin, gums, and joints, followed by death. At about that
zymes participate in the major oxidation and reduction time, Captain James Cook showed that sailors could avoid
processes of cells. Some assist in the making and break- scurvy during long voyages by eating local green vegeta-
ing of carbon–carbon bonds. Others are carriers of molec- bles and grasses. Soon thereafter British seamen became
ular fragments. Coenzymes participate in virtually every “limeys.” The chemical structure of the active component,
aspect of the chemistry of every living cell whether of vitamin C (Fig. 1), was established in 1933. In a similar

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