ANEURINE (thiamine) 



rate of disappearance of pyruvate, however, was increased by the 

 addition of magnesium and potassium ions even in the absence of 

 vitamin B^, but the oxygen uptake was not increased. This observa- 

 tion probably explains the acceleration that takes place in the oxida- 

 tion of lactate by vitamin Bi-deficient bacteria in the presence of 

 magnesium and potassium ions and in the absence of aneurine, since 

 the removal of pyruvic acid by these ions would enhance the oxidation 

 of lactate, which it is known to inhibit. The oxygen uptake, with 

 succinate and fumarate as substrates, was also greatly increased by 

 magnesium and potassium ions, even in the absence of aneurine. 

 This is explained by the fact that these ions accelerate the breakdown 

 by propionic acid bacteria of oxaloacetate, which inhibits succinate 

 oxidation. Since it is known that oxaloacetate inhibits succinic 

 dehydrogenase, this also explains the effects of cozymase and nicotin- 

 amide on succinate oxidation by animal tissues. Thus the breakdown 

 of both oxaloacetate and of pyruvate by propionic acid bacteria is 

 catalysed by a mixture of magnesium and potassium ions indepen- 

 dently of the presence of vitamin B^. The accelerating effects of 

 vitamin B^ in the absence of magnesium and potassium ions are 

 explained as due to the catalysed oxidation of pyruvate or acetate 

 formed from the substrate as intermediaries. 



Quastel and Webley also found that the rate of oxidation of 

 acetate, succinate, etc., by vitamin B^-deficient propionic acid bac- 

 teria could be increased not only by the addition to these substrates 

 of magnesium and potassium ions or hexosediphosphate ions (which 

 had the same effect), but also by previously incubating the organisms 

 with these ions, followed by thorough washing. They suggested that 

 the ions completed or induced the formation in the bacterial cell of a 

 system essential for the oxidation of the substrates. 



These results may be accounted for on the assumption that incu- 

 bation of the propionic acid bacteria with hexosediphosphate enriches 

 the cells with adenosine triphosphate and that such cells then have 

 the ability to phosphorylate vitamin B^ ; the cocarboxylase so formed 

 then catalyses the oxidation of pyruvate and acetate. The magnesium 

 ions are believed to be necessary for effecting phosphorylation. 



The fact that succinate, fumarate and ethyl and propyl alcohols 

 do not require aneurine for their oxidation is explained by assuming 

 that adenosine triphosphate is essential either for their complete 

 oxidation or for their oxidation to pyruvate or acetate, where 

 cocarboxylase becomes necessary. Thus, adenosine triphosphate 

 is a coenzjmie for the oxidation of fumarate, ethyl and propyl 

 alcohols. 



The suggestion made by Krebs and Eggleston and by Smyth that 

 vitamin Bi catalysed the formation of oxaloacetate was regarded by 



98 



