vitamin B complex 548v
blindness. The role of vitamin A in
other aspects of metabolism is less
clear.
A- Information about IUPAC nomenclature
vitamin B complexA group of
water-soluble vitamins that charac-
teristically serve as components of
*coenzymes. Plants and many mi-
croorganisms can manufacture B
vitamins but dietary sources are es-
sential for most animals. Heat and
light tend to destroy B vitamins.
Vitamin B 1 (thiamin(e)) is a precur-
sor of the coenzyme thiamine py-
rophosphate, which functions in
carbohydrate metabolism. DeÜciency
leads to beriberi in humans and to
polyneuritis in birds. Good sources
include brewer’s yeast, wheatgerm,
beans, peas, and green vegetables.
Vitamin B 2 (riboÛavin) occurs in
green vegetables, yeast, liver, and
milk. It is a constituent of the coen-zymes *FAD and FMN, which have
an important role in the metabolism
of all major nutrients as well as in
the oxidative phosphorylation reac-
tions of the *electron transport
chain. DeÜciency of B 2 causes inÛam-
mation of the tongue and lips and
mouth sores.
Vitamin B 6 (pyridoxine) is widely
distributed in cereal grains, yeast,
liver, milk, etc. It is a constituent of a
coenzyme (pyridoxal phosphate) in-
volved in amino acid metabolism.
DeÜciency causes retarded growth,
dermatitis, convulsions, and other
symptoms.NNC
H 2SNCH 23 CH NH (^22) CH OH
CH 3
Vitamin B 1
N
N
N
NH
O
O
3 CH
3 CH
2 CH
2 CH
OH
OH
OH
OH
Vitamin B 2
N
CH 3
OH
HOH 2 C
CH 2 OH
Vitamin B 6
Vitamin B 12 (cyanocobalamin;
cobalamin) is manufactured only by
microorganisms and natural sources
are entirely of animal origin. Liver is
especially rich in it. One form of B 12
functions as a coenzyme in a number
of reactions, including the oxidation
of fatty acids and the synthesis of
DNA. It also works in conjunction
with *folic acid (another B vitamin)
in the synthesis of the amino acid
methionine and it is required for nor-
mal production of red blood cells.
Vitamin B 12 can only be absorbed