ANALOGS OF PYRIDOXAL 575 



tabulation) (Jacobs et al., 1960). These results definitely implicate pyridoxal 

 in amino acid transport but do not prove that it functions directly in the 

 transport mechanism, since the effect could be an indirect one. 



Pyridoxol Deoxypyridoxol % Change in transport 



- - —56 



+ — +25 



+ -35 



+ + +6 



The uptake of glycine by ascites carcinoma cells is inhibited by 5-25 mM 

 deoxypyridoxol (Christensen et al., 1954). Since pyridoxine deficiency re- 

 duces the accumulating ability and this is restored by pyridoxal in vitro, 

 it would appear that pyridoxal functions here in some manner, although 

 again not necessarily in the membrane transport system. 



Effects on Growth 



Deoxypyridoxol suppresses the growth of a variety of microorganisms. 

 Rabinowitz and Snell (1953 a) emphasized that sensitive organisms are 

 those requiring an exogenous source of pyridoxine, and in these the inhibi- 

 tion can be counteracted by pyridoxine; those synthesizing their own p\Ti- 

 doxal can effectively resist the analog. The situation is quite complex, how- 

 ever, and when different analogs are examined a marked variability in sus- 

 ceptibility is found (Rabinowitz and Snell, 1953 b). For example, w-me- 

 thylpyridoxol is inhibitory to yeast but not at all to Streptococcus faecalis or 

 Lactobacillus helveticus, the 5-deoxypyridoxol derivatives being the most ef- 

 fective in these latter organisms; in L. helveticus, only 5-deoxypyridoxol is 

 inhibitory, 4-deoxypyridoxol, 5-deoxypyridoxol, and 5-deoxypyridoxamine 

 being without action. A factor that is very important in determining the 

 susceptibility of bacteria to these analogs is the nature of the exogenous 

 amino acids supplied. Streptococcus faecalis grows well if all amino acids are 

 provided even though pyridoxine is absent, but a requirement for pyrido- 

 xine and a sensitivity to analogs are created by restriction of the amino 

 acids in the medium (Olivard and Snell, 1955). Under certain circumstances 

 the growth can be limited by conversion of l- to D-alanine by alanine race- 

 mase, which involves pyridoxal-P and is quite sensitive to 5-deoxypyridoxol 

 {K, = 0.089 mM) and w-methylpyridoxol {K^ = 0.53 mM). The inhibition 

 of growth by these analogs can be explained on the basis of the inhibition 

 of this enzyme under these conditions. On the other hand, in most circum- 

 stances the inhibition must be on amino acid metabolism, as in Vibrio 



