Vitamin B6: pyridoxine, pyridoxal, pyridoxamine

The term vitamin B6 is now properly used, according to a decision of the American Society of Biological Chemists, to designate three naturally occurring substances: pyridoxine, pyridoxal and pyridoxamine. The formulae of these substances are given below:

Pyridoxine is 2-methyl-3-hydroxy-4,5-dihydroxymethyl pyridine. Pyridoxal is the aldehyde derivative of pyridoxine and has a formyl group instead of a hydroxymethyl group at the 4 position. Pyridoxamine is an amino derivative and has an amino methyl instead of a hydroxymethyl group at the 4 position. The three forms of the vitamin are almost equally effective for higher animals, but some bacteria
have specific requirements for one form or the other. Vitamin B 6 is needed by many bacteria, by some protozoa, and by most of the insects whose vitamin requirements have been investigated.

When rats are deprived of vitamin B 6, they develop a painful inflammation of the skin. This is especially evident in the skin of the extremities--the paws, snout, and ears. The ailment is sometimes called rat acrodynia because of a supposed similarity to a human ailment in which the nerves and skin of the hands and feet are affected. The disease is not wholly specific for vitamin B 6 deficiency; it can be produced also in other ways, for example by a lack of unsaturated fatty acids. In various higher animals, convulsions may follow extreme vitamin B 6 deficiency. Sometimes lack of the vitamin causes muscular weakness; it can also cause anemia.

Vitamin B 6 deficiency can be induced by the addition of an antagonistic analogue, desoxypyridoxine. Thus if this compound is injected into hens' eggs, the embryos do not proceed very far in their development.

Vitamin B 6 is important for the proper metabolism of the amino acids. It forms part of an enzyme system which promotes the synthesis of amino acids by the addition of carboxyl groups. Acting as part of what is presumably the same enzyme system, the vitamin also favors the removal of carboxyl groups from amino acids. Another type of enzyme for which vitamin B 6 is an important constituent is transaminase. This enzyme catalyzes the transfer of an amino group from one amino acid to another; an important type of reaction in protein metabolism. Thus there is some important information as to how the vitamin functions with respect to the chemical reactions occurring during the metabolism of proteins and amino acids, but how this is related to the disturbances which occur in skin, nerves, muscle and blood when the vitamin is lacking has yet to be explained. It has been claimed, on the basis of isolation studies of mitochondria, that these granules contain especially large amounts of vitamin B 6. However, it is the nucleoprotein-containing granules of the cytoplasm that are believed to be especially important for protein metabolism.