566 



2. ANALOGS OF ENZYME REACTION COMPONENTS 



ulation) and noted that only the phosphorylated derivatives are signifi- 

 cantly inhibitory. Whether inhibition of these oxidases by analogs plays a 

 role in the depressant or toxic effects produced is at present unknown, but 

 it must be admitted that for deoxypyridoxol and its phosphate none of 

 the inhibitions is probably potent enough to be important in vivo. 



The effects of analogs on the tissue levels of the vitamin Bg group are 

 particularly important in certain arguments relative to the mechanisms by 

 which these analogs are toxic. Umbreit (1955 a) believes that deoxypyri- 

 doxol exerts actions other than the antagonism of vitamin Bg function. 

 The basis for this is principally that deoxypyridoxol accelerates the ap- 

 pearance of deficiency symptoms when animals are on a diet lacking pyri- 

 doxine and yet does not reduce the tissue levels of pyridoxal coenzymes. 

 He has also pointed out that in some cases there is also no fall in transamin- 

 ase or decarboxylase activity during the "acute" deficiency produced by 

 deoxypyridoxol. Nevertheless, it is admitted that the toxic effects of de- 

 oxypyridoxol can be readily counteracted by pyridoxine administration. 

 Actually there is very little published on tissue levels of vitamin Bg as af- 

 fected by deoxypyridoxol. Stoerk (1950) reported that dietary deficiency 

 lowers liver pyridoxine content but that deoxypyridoxol produces no fur- 

 ther lowering despite a more rapidly appearing deficiency syndrome. Similar 

 results were obtained by Beaton and McHenry (1953) in rats exhibiting 

 acrodynia following deoxypyridoxol feeding (see accompanying tabulation). 

 Umbreit also cites unpublished data supporting these results. Effects of 

 deoxypyridoxol on enzyme activity in vivo will be taken up in the following 



