THE VITAMIN Be GROUP 655 



aldehyde which have been given the trivial names, pyridoxamine and 

 pyridoxal, respectively. 



CH 2 NH 2 CHO 



— CH 2 OH HO-< ^— CH 2 OH 



pyridoxamine pyridoxal 



On the basis of their structures, Snell 35 proposed that pyridoxal and 

 pyridoxamine might have a role in biological transamination, and showed 

 that reversible interconversion of pyridoxal and pyridoxamine occurred 

 by transamination reactions with amino acids. 37 Vitamin B 6 -deficient 

 rats were found to have a marked decrease in transaminase activity com- 

 pared to normal rats. 38 



Pyridoxal, but not pyridoxamine, added to cells of Streptococcus 

 faecalis R stimulated tyrosine decarboxylase, 39 which was previously 

 known to be influenced by the concentration of pyridoxine added to the 

 growth medium. 40 Gunsalus, Bellamy and Umbreit 41 subsequently found 

 that adenosine triphosphate was essential for maximum activity of 

 pyridoxal in the system, and prepared a phosphorylated derivative of 

 pyridoxal which was active in the absence of the phosphorylating agent. 

 The enzyme was later isolated in a cell-free state and resolved into an 

 apoenzyme and a coenzyme. The coenzyme was replaced by the phos- 

 phorylated pyridoxal. 42 One of the methods of preparation 41 indicates 

 that the 5-hydroxymethyl is the point of phosphorylation, but definite 

 proof of the structure is still lacking. 41 * This pyridoxal phosphate has 

 been found to be a prosthetic group of transaminase and other enzymes 

 (p. 177) , and can be converted by heating with glutamic acid to pyridox- 

 amine phosphate, which functions as a cotransaminase but not as a 

 codecarboxylase. 43 The discovery of this group of factors, which have 

 been termed the vitamin B 6 group, stimulated studies of comparative 

 activities which are indicated in Table 36. 



Injected pyridoxine, pyridoxal and pyridoxamine are equally active 

 for dogs, rats and chicks; however, either pyridoxal or pyridoxamine 

 is less active than pyridoxine for rats, mice and chicks when mixed with 

 the diet. This loss of activity is prevented in the case of rats and 

 chicks when these substances are fed by dropper. A possible explanation 

 has been suggested 45 that pyridoxal and pyridoxamine are more suscept- 

 ible to destruction or utilization by intestinal bacteria than is pyridoxine. 

 This conclusion is supported by the fact that Streptococcus faecalis R and 

 presumably many other bacteria do not remove appreciable amounts of 



