PYRIDOXINE 



the " synthetic " codecarboxylase prepared from pyridoxal functioned 

 as a coenzyme for all four amino acid decarboxylases. 



Pyridoxine, pyridoxal and pyridoxamine were all converted into 

 codecarboxylase by micro-organisms that utilised them as a source of 

 vitamin Bg ; it was shown that with S. faecalis R the conversion of 

 pyridoxamine into codecarboxylase required the presence of a keto- 

 acid (see page 300). Organisms that grew in the absence of vitamin 

 Bg were able to synthesise codecarboxylase, whilst the codecarboxylase 

 content of rat tissue was dependent on the pyridoxine intake. ^^ 



The properties of synthetic codecarboxylase were described by 

 Gunsalus et al}^ 



J. Baddiley and E. F. Gale ^^ prepared several cell-free amino acid 

 decarboxylases and resolved those responsible foi the decarboxylation 

 of L-lysine, L- tyrosine, L-arginine and L-ornithine into specific 

 apoenz5mies and a common coenzyme, a concentrate of which was also 

 prepared from yeast. The decarboxylases for L-histidine and L-glut- 

 amic acid did not appear to contain the coenzyme. Pyridoxal phos- 

 phate was found to act as a coenzyme for the decarboxylases of 

 L-lysine, L-tyrosine, L-arginine and L-ornithine. Lichstein et al}^ 

 confirmed the observation that pyridoxal phosphate functioned as a 

 coenzyme for L-ornithine decarboxylase and showed that it was also 

 the coenzyme of L-dihydroxyphenylalanine decarboxylase. 



P. Karrer and M. Viscontini ^* suggested that the preparations of 

 pyridoxal phosphate used by other workers were impure and that 

 their biological activity was due to some other constituent. They 

 therefore synthesised pyridoxal-3-phosphate acetal : 



(H0)20P-0^ ^CHgOH 



CH, 



CH(OC2H5 



and pyridoxal-3-phosphate and claimed that both served as coenzymes 

 for L-tyrosine decarboxylase prepared from S. faecalis, and for L-lysine, 

 L-arginine and D-glutamic acid decarboxylases prepared from three 

 strains of Escherichia coli. According to L C. Gunsalus and W. W. 

 Umbreit,^^ however, synthetic pyridoxal-3-phosphate acetal does not 

 catalyse the decarboxylation of tyrosine, and pyridoxal-3-phosphate 

 has only i /2000th to 1 /3000th of the activity of the natural coenzyme, 

 the apparent codecarboxylase activity of Karrer and Viscontini's 

 compounds being due to faulty testing technique. Synthetic pyri- 

 doxal-5-phosphate, on the other hand, catalysed both the decarboxyla- 

 tion of tyrosine and, at a higher concentration, the glutamic-aspartic 

 transamination (page 333). Using acetone-dried vitamin Bg-free cells 



332 



