ANEURINE (thiamine) 



Compounds related to Folic Acid 



According to Busnel et al.,^^ the growth of vitamin Bi-deficient 

 pigeons is accelerated by several substances related to folic acid (see 

 page 513), namely, isoxanthopterin, 2 : 6-dihydroxy-8 : 9-dimethyl- 

 pteridine, 2-amino-6-hydroxy-8 : 9-dimethylpteridine and desiminoiso- 

 xanthopterin-carboxylic acid ; these had approximately one-tenth the 

 activity of aneurine. Fluorescyanine, from carp-scales, had a similar 

 action to aneurine, although much weaker, in Peter's catatorulin test 

 (page 28). All the above substances and, in addition, xanthopterin- 

 carboxylic acid and isoxanthopterin-carboxylic acid maintained 

 normal growth and chronaxia in young rats deprived of aneurine. 

 None of them, however, stimulated the growth of Polytomella caeca 

 deprived of aneurine. So far, these results remain unconfirmed but, 

 in view of the observations with P. caeca, it is unlikely that the effect 

 is due to the presence of true vitamin Bj activity in the folic acid 

 analogues. 



Pyrithiamine 



Pyri thiamine, the pyridine analogue of aneurine prepared by 

 A. H. Tracy and R. C. Elderfield,^^ was without growth-promoting 

 properties, as has already been noted (see page 123). Nevertheless 

 it is a most interesting substance, as it inhibits the growth of several 

 micro-organisms for which aneurine is an essential growth factor. 

 Thus O. Wyss ^* showed that it interfered competitively with the 

 utilisation of aneurine by Staphylococcus aureus, the addition of 

 aneurine counteracting the inhibition due to pyrithiamine. This is an 

 instance of competition between a growth factor and a growth in- 

 hibitor of analogous chemical structure, of which the vitamin B 

 complex provides many other examples (see pages 292, 345, 397, 546). 



To neutralise the growth-stimulating effect of one molecule of 

 aneurine on 5. aureus, 666 to 750 molecules of pyrithiamine were 

 required, a value similar to that observed for sulpha pyridine and 

 ^-aminobenzoic acid. For E. colt, the ratio between the amounts of 

 growth inhibitor and growth factor that just counterbalanced one 

 another was 20,000. Pyrithiamine is therefore a much less efficient 

 antagonist towards aneurine for E. coli than for 5. aureus. Similar 

 variations with different organisms have been noted with other pairs 

 of growth factors and inhibitors. 



D. W. Woolley and A. G. C. White ^^ correlated this difference in 

 the response of different organisms with their requirements for 

 aneurine. Organisms that required the intact aneurine molecule 

 were inhibited by smaller amounts of pyrithiamine than organisms 



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