Agriculture Reference
In-Depth Information
polishings that was effective in preventing or curing this disease. Funk believed this
was a vital amine and coined the term “vitamines” to include this and other, yet-to-
be-identified, vital factors. The “e” was dropped when it was established that not all
vitamins contained amine groups. E. V. McCollum and associates concluded in 1916
from their studies with purified diets (begun at least 3 years before) and from studies
of others that there was an unidentified fat-soluble A (needed for growth and preven-
tion of xerophthalmia) and an unidentified water-soluble B, which eventually proved
to be the antiberiberi factor found by Funk. Thiamin (B
1
) was isolated in 1926 and
its structure established in 1936.
Pellagra, a disease characterized by dermatitis, gastrointestinal problems, and
mental disturbances, was commonly observed in the early 1900s, particularly in the
southern United States where corn was a dietary staple, and meat and milk intakes
were limited. Although some proposed that it was infectious or caused by a patho-
genic mold, Joseph Goldberger and associates, using a dog model, showed in 1928
that pellagra could be cured by yeast. Following isolation of a known chemical,
nicotinic acid, from yeast, it was established in 1937 that either nicotinic acid or
nicotinamide (jointly designated niacin) were effective antipellagrins. Later, it was
found that corn is low in tryptophan, an amino acid that can serve as a precursor for
niacin synthesis in animal tissues (if the tryptophan supply is adequate). In addition,
an appreciable amount of the niacin in corn is bound and unavailable for absorption
unless treated with alkali, as in production of tortillas.
Some patients with pellagra still showed lesions about the mouth (cheilosis) even
after treatment with niacin. Yeast that had been autoclaved lost its thiamin activity
but still was effective against these lesions. The effective agent was termed B
2
but
was soon found to be a complex of factors. The agent effective against cheilosis was
identical with a greenish-yellow fluorescent pigment isolated from whey in 1935 and
was subsequently named riboflavin.
Again, yeast proved useful when in 1931 it was found to cure a macrocytic anemia
of pregnancy commonly seen in Mohammedan women in Bombay, India. Lucy Wills
induced this anemia, and a leukopenia, in rhesus monkeys fed a poor Bombay diet.
These conditions responded to extracts from yeast or from liver but did not respond
to any of the then-known vitamins. The effective factor was temporarily designated
vitamin M for monkey. By 1944, it was established that a compound isolated from
spinach supported growth in bacteria and in chicks and prevented macrocytic ane-
mia in the latter. It was named folic acid from its origin in foliage.
The 1930s and 1940s were a particularly active period in vitamin research, and
additions to the water-soluble list by 1937 included pantothenic acid, pyridoxine (B
6
),
and biotin. A fat-soluble dietary factor shown in 1922 to be required for reproduction
by rats, and eventually to prevent certain muscular dystrophies, was named vitamin
E and was isolated in 1935. Another fat-soluble vitamin, found by Henrik Dam in
1935 to prevent hemorrhages in chicks, was named vitamin K (for “koagulation” in
Danish). The last on the list of generally accepted vitamins, isolated in 1948, was
water soluble, contained cobalt, and was named vitamin B
12
. It was found in ani-
mal tissues, soil, and certain bacteria but not in higher plants. If the diet contained
adequate cobalt, microorganisms in the rumen of cattle or sheep, or in the cecum and
