Function of the vitamin B6 group; pyridoxal phosphate (codecarboxylase) in transamination.

Vitamin Be has for some time been implicated in protein metabolism. More recently a specific function of pyridoxal in the coenzome of tyrosine decarboxylase has been found (l), and the discovery of this function extended to include amino acid decarboxylases in general (2, 3). All members of the vitamin Be group (pyridoxine, pyridoxal,” pyridoxamine) are converted into this coenzyme (termed codecarboxylase (4) in recognition of its function in amino acid decarboxylases) by those organisms using them as a source of vitamin Be (5). The amino acid decarboxylases so far shown to require the coenzyme include tyrosine (2, 5, S), lysine (7), arginine (2, 3), ornithine (2), glutamic acid (3), and dopa (3, 4-dihydroxyphenylalanine2). The exact structure of the coenzyme is not certain but the properties are sufficiently well known to indicate that it is a phosphorylated derivative of pyridoxal and to suggest the possible posit.ion of linkage. The naturally occurring and the synthetic preparations of coenzyme, which possess similar properties (2, S), are referred to here as pyridoxal,phosphate, or codecarboxylase, without further specification of structure. The function of codecarboxylase in amino acid decarboxylation assures it a place in any consideration of protein metabolism but does not necessarily mean that this is the only function of the vitamin Bg group. Schlenk and Snell (9) have recently reported that tissues of rats on a vitamin Be-deficient diet possess low transaminase activity as compared with those of animals supplied adequate amounts of vitamin Bs. The transamination rate of deficient tissues could at times be stimulated by the addition of pyridoxal and adenosine triphosphate, a procedure known to activate the tyrosine decarboxylase system of dried cell preparations of Streptococcus faecalis (6). Snell (10) has also demonstrated interconversion of pyridoxal and pyridoxamine by heating with amino and keto acids respectively, and has