FUNCTION 



Furthermore, administration of L-tryptophan reduced the sur- 

 vival time of vitamin Bg-deficient mice, but to a smaller extent than 

 did casein containing the same amount of tryptophan, suggesting that 

 other amino acids contributed to the phenomenon. Tyrosine and 

 histidine, however, were without effect ; so was phenylalanine, although 

 it gave rise to a urinary chromogen the excretion of which was un- 

 affected by pyridoxine. Cystine and methionine reduced the survi\al 

 time of vitamin Bg-deficient rats.^° 



The amount of xanthurenic acid excreted by pigs was also increased 

 when the animals were fed on a vitamin Bg-deficient diet,* and high 

 xanthurenic acid excretion was generally associated with faulty 

 tryptophan metaboHsm. Again, pigs maintained on a diet in which 

 nitrogen was supplied in the form of an acid hydrolysate of casein or 

 as zein, neither of which contains tryptophan, failed to grow and 

 developed a normocytic or microcytic normochromic anaemia, similar 

 to that observed in vitamin Bg-deficient pigs.^ 



Decarboxylation of Amino Acids 



A further advance was made when I. C. Gunsalas and W. D. 

 Bellamy ® observed that tyrosine decarboxylase (prepared from 

 Streptococcus faecalis R) was stimulated by yeast extract, by pyri- 

 doxal (but not pyridoxamine) and by solutions of pyridoxine treated 

 with cystine or hydrogen peroxide. The activity of each preparation 

 was proportional to its " pseudo-pyridoxine " content, as determined 

 microbiologically. 



Pyridoxal, however, only became an effective coenzyme in presence 

 of adenosine triphosphate,'^ and the actual coenzyme was therefore 

 presumed to be a phosphorylated pyridoxal, possibly : 



(H0)20P« 



A phosphate was synthesised by treating pyridoxal with thionyl 

 chloride and reacting the product with silver dihydrogen phosphate, 

 or by treating pyiidoxal in the cold with phosphoric acid. 



Cell-free tyrosine decarboxylase was prepared from 5. faecalis R 

 and resolved into its apoenzyme and coenzyme. The latter was 

 identified as a derivative of pyridoxal.^ W. W. Umbreit and L C. 

 Gunsalus ^ then showed that arginine and glutamic acid decarboxyl- 

 ases, prepared from Escherichia coli, could be activated by the same 

 coenzyme that activated lysine and tyrosine decarboxylases, and that 



331 



