FUNCTION 



Quastel and Webley as untenable because oxaloacetate cannot replace 

 aneurine as an accelerator of acetate and propionate oxidation by 

 propionic acid bacteria. Thus, aneurine exerts its catalytic effect on 

 acetate and pyruvate oxidations by a process other than by the forma- 

 tion of oxaloacetate as suggested by Krampitz and Werkman. 



Aneurine, a Catalyst for Several Reactions 



The most recent results favour the view, which now enjoys wide 

 support, that aneurine, or rather cocarboxylase, is capable of catalysing 

 more than one reaction involving pyruvic acid. F. Lipmann,^® for 

 example, suggested that in lactic acid bacteria, such as B. delbruckii, 

 it functioned as a dehydrogenating catalyst promoting reaction (i), 

 whereas in yeast it catalysed reaction (2). He showed ^^ that, on 

 hydrogenation in presence of platinum black or on reduction by 

 sodium dithionite, hydrogen was taken up by the quaternary 

 nitrogen atom of the thiazole ring, giving dihydroaneurine pyrophos- 

 phate : 



CH3 



+ yC==C . CHa . CH2 . OP^OeHa ^L!^ 



CH3 . C C— CH2— N< I 



N=C.NH, 



N— CH 

 N=:C . NH2 



CH3 



.C C . CHa . CHa . OPaOeHa 



CH3— € C— CH,— N< I 



II I \CH,-S 



N— CH 



He drew an analogy with the reduction of Warburg's yellow enzyme 

 and suggested that such a change may occur in vivo as well as i7t vitro. 

 In pigeon brain tissue, however, cocarboxylase appears ^^ to catalyse 

 the dismutation reaction (3). 



Lipmann's views were supported by E. S. G. Barron and C. M. 

 Lyman, ®^ who observed that the extent to which cocarboxylase 

 catalysed the oxidation of pyruvic acid on the one hand, and its dis- 

 mutation on the other, varied with -different organisms according to 

 the oxygen tension. Thus, under optimal conditions for oxidation, 

 pyruvic acid was directly oxidised to acetic acid and carbon dioxide ; 

 under optimal conditions for reduction it might be reduced to lactic 

 acid or split by dismutation into acetic acid and formic acid : 



CH3 . CO . COOH 4- H2O -> CH3 . COOH + H . COOH 



The " oxydismutation coefficients ", i.e. the ratio between the 

 amount of pyruvic acid used by the cell under conditions optimal for 



99 



