FUNCTION 



pyridoxal and, to test this, A. E. Braunstein and M. G. Kritzmann ^s 

 studied the effect of different factors on the reaction : 

 L-aspartic acid + pyruvic acid >■ L-alanine + oxaloacetic acid. 



They found that co-aminopherase and natiural codecarboxylase 

 (prepared by E. F. Gale) were active, but that pyridoxal phosphate, a 

 co-aspartic acid aminopherase concentrate purified by a method used 

 successfully for the purification of codecarboxylase, ^^ and boiled 

 glutamic acid aminopherase were inactive. Thus the coenzyme 

 system of mammalian aspartic acid aminopherase appeared to be 

 different from, or more complex than, pyridoxal phosphate. This was 

 confirmed by E. F. Gale and H. M. R. Tomlinson,^^ who tested the 

 activity of various factors as tyrosine codecarboxylases and found 

 that, whereas pyridoxal phosphate and codecarboxylase were active, 

 three co-aspartic acid aminopherases prepared by Braunstein and 

 Kritzmann were inactive. On the other hand, two glutamic acid 

 aminopherases prepared by the Russian workers were markedly active. 



It was then shown by M. G. Kritzmann and O. Samarina ^o that 

 glutamic acid aminopherase, after inactivation by acid or alkali, 

 could be reactivated to the extent of 20 to 70 % by the addition of 

 boiled muscle or liver extract, or of small amounts of pyridoxal phos- 

 phate, although larger amounts proved to be inhibitory. Green et 

 al}^ then suggested that aspartic acid-aminopherase activity might 

 be due to a combination of glutamic acid-aspartic acid and glutamic 

 acid- alanine transaminases, with glutamic acid or a-ketoglutaric acid 

 as the links joining the two systems ; D. E. O'Kane and I. C. 

 Gunsalus ^^ actually reproduced the activity of aminopherase by 

 means of a mixture of the two transaminases, together with p5a-idoxal 

 phosphate and glutamic acid. Thus the so-called aminopherase is 

 really a transaminase of which the prosthetic group is, once again, 

 pyridoxal phosphate. 



Tryptophan Synthesis 



The third enzyme system with which pyridoxine is associated is 

 one responsible for the synthesis of tryptophan, for pyridoxal phos- 

 phate was shown ^^ to be the prosthetic group of an enzyme present 

 in Neurospora that converted indole and serine into tryptophan : 



HOCH2.CH.COOH 

 NH2 



XX-NH^ 



-CH, . CH . COOH 



" I 

 NH2 



The enzyme wa.s resolved into its apoenzyme and coenzyme, and 

 pyridoxal phosphate was shown to be capable of replacing the coenzyme 



335 



