PYRIDOXINE 



References to Section 14 



1. K. Unna and W. Antopol, Proc. Soc. Exp. Biol. Med., 1940, 43, 



116. 



2. C. G. Weigand, C. R. Echler and K. K. Chen, ihid., 147. 



3. N. W. Shock and W. H. Sebrell, Amer. J. Physiol., 1946, 146, 399. 



15. FUNCTION OF PYRIDOXINE AND RELATED C02V1P0UNDS 



Pyxidoxine, pyridoxal and pyridoxamine are now known to be 

 concerned with the decarboxylation of amino acids, and with the 

 transamination mechanism. All three compounds are apparently 

 equally effective for both systems in rats, moulds and some yeasts, 

 and are probably inter-convertible in these organisms. For many 

 lactic acid bacteria, on the other hand, pyridoxal and pyridoxamine 

 (" pseudo-pyridoxine ") are up to 1000 times as effective as pyri- 

 doxine ; ^ such organisms presumably are very inefficient in convert- 

 ing pyridoxine into the biologically active derivative. A third system 

 for which a compound related to pyridoxine is essential is one that 

 controls red blood cell formation. Each of these three functions will 

 be considered in turn. 



Protein Metabolism 



Reference has already been made (page 318) to the fact that 

 vitamin Bg deficiency results in an increase in the body protein, that 

 the protein content of the diet affects the severity of the symptoms of 

 pyridoxine deficiency and that nitrogen metabolism is upset in pyri- 

 doxine-deficient rats, mice and dogs. Subsequently, a connection 

 was established between vitamin Bg and tryptophan. Lepkovsky et 

 al.^ noted that tryptophan metabolism differed in the dog and the rat 

 and that the difference was paralleled by a difference in the symptoms 

 of vitamin Bg deficiency in the two species ; the dog developed a 

 severe anaemia and excreted little xanthurenic acid, whereas the rat 

 developed only a mild anaemia and excreted large amounts of xan- 

 thurenic acid. 



Vitamin Bg-deficient mice also excreted xanthurenic acid, and 

 the amount varied with the quantity of casein or tryptophan in the 

 diet.^ Moreover, the more casein was added to the diet, the sooner 

 did the animals die. The amount of chromogen excreted was reduced 

 by administration of pyridoxine, but the amount needed to restore 

 the level of excretion to normal was three times as much with 60 % 

 as with 20 % of casein. 



330 



