PYRIDOXINE 



obtained from pig heart ; these effected the transfer of the amino 

 group from glutamic acid to oxaloacetic acid, the reverse transfer 

 from aspartic acid to a-ketoglutaric acid/^' ^^ the transfer from 

 glutamic acid to succinic acid and from alanine to a-ketoglutaric 

 acid.^^ The precise structure of the phosphate is not known, but 

 pyridoxal-3-phosphate acetal had no coenzyme activity. 



That a phosphate of pyridoxal is the coenzyme of at least two 

 transaminases was also demonstrated by M. G. Kritzmann and O. 

 Samarina,^^ who found that pyridoxal phosphate would partially re- 

 activate glutamic acid- alanine transaminase from pig heart, and by 

 D. E. O'Kane and I. C. Gunsalus,^^ who prepared a very pure specimen 

 of the transaminase apoenzyme, and showed that a pyridoxal phosphate 

 of uncertain constitution functioned as its coenzyme. According to 

 F. Schlenk and A. Fisher,^^ some transaminase preparations contain 

 pyridoxamine as well as pyridoxal derivatives, whilst J. C. Rabinowitz 

 and E. E. Snell ^3 isolated a substance that appeared to be pyridox- 

 amine phosphate from yeast, liver and dried grass, and found that when 

 pyridoxal phosphate was heated with glutamic acid, quantitative 

 conversion to pyridoxamine phosphate occurred. The product stim- 

 ulated the glutamic acid- aspartic acid transaminase of dried 5. faecalis 

 but not the corresponding (purified) apoenzyme from pig heart or 

 tyrosine decarboxylase, both of which are activated by pyridoxal 

 phosphate. 2^* 



The transaminase activities of heart and kidney tissues from 

 vitamin Bg-deficient rats fell to 40 % of their original value, and 

 were restored to normal by the addition of pyridoxal phosphate or 

 pyridoxamine phosphate. Pyridoxal and pyridoxamine, however, 

 had no effect even in presence of adenosine triphosphate.^* 



Transaminases have been shown to be present in seeds. Wheat 

 germ, for example, contained enzymes that catalysed both the glut- 

 amic acid-aspartic acid and glutamic acid-alanine transformations. ^^ 

 The enzymes were present in the leaves, stems, roots, fruit and nodular 

 tissue. 



Aminopherase Activity 



Closely related to the transaminases is another enzyme system, 

 known as aspartic acid aminopherase, or aspartic acid-alanine trans- 

 aminase. According to M. G. Kritzmann, ^^ this catalyses the trans- 

 amination reaction between L-aspartic acid and pyruvic acid, in 

 presence of a dialysable coenzyme, to give alanine. Concentrates of 

 the coenzyme, co-aminopherase, were prepared from pig heart and 

 shown to be labile to acid.^^ The close relationship between this 

 coenzyme and other co-transaminases suggested that it might contain 



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