110 BACTERIOLOGICAL CHEMISTRY 



which occurs in the vitamin B complex. It maj^ also be 

 concerned as an anti -pernicious ansemia factor in liver 

 extracts. It has been isolated from rice bran, liver, 

 molasses and similar sources. It was shown by Williams 

 to be necessary for the growth of Saccharomyces cerevisice 

 and Strej^tobacterium plantarum. It is required by Lacto- 

 hacilhis casei, L. delhrilckii and L. lactis but not by L. 

 arabinostis or L. pentosus. Leuconostoc mesenteroides can 

 grow without it but is stimulated by its presence. The 

 last three organisms are able to synthesise pyridoxine 

 but L. mesenteroides only to the extent of about one- 

 fourth of the production by the other two. The amount 

 required by L. casei depends on the oxygen tension of 

 the medium, the lower the oxygen tension the lower is 

 the amount of pyiidoxine required. It stimulates the 

 growth of staphylococci. 



The 4:5-diacetyl derivative is nearly as active as 

 pyridoxine itself, but the triacetyl derivative is inactive. 

 Substitution usually reduces or destroys the activity. 



It has been shown that pseudopyridoxine, which is 

 form.ed by the action of hydrogen peroxide on pyridoxine 

 or by autoclaving solutions of the latter in presence of 

 cystine, is considerably more active than pyridoxine in 

 stimulating the growi:,h of Str. lactis and L. casei, although 

 it had no greater effect on the growth of several moulds, 

 N euros fora sitophila, yeasts such as Saccharomyces 

 carlshergensis and Sacch. oviformis or rats. 



Pseudoj)yridoxine is now known to be a mixture of 



CHO CH.NH2 



HO |/\, CH2OH , HO (^\ CH2OH. 



pyridoxal ^^^ 



CH3 'J pyridoxamine, CH3 



N N 



These two compounds are reversibly interconvertible and 

 act as the co-enzyme of transamination (see p. 341). 



