IV. BIOCHEMICAL SYSTEMS 441 



system w ith the \itamiii. In 1938, however, Lipmann and Perlman** showed 

 that the activity of thiamine was lost after dehydrogenation. Stern and 

 Mehiick^*^ pointed out that the sulfite, formed in the reaction of thiamine 

 with sodium cHthionite, must split the vitamin molecule (Williams cl al.^^). 

 'I'his was proved by Karrer et al.^* and Karrer and Viscontini.''^ Further- 

 more, Stern and Melnick'"' showed that reduction of thiamine with activated 

 hydrogen gave a product that was not autoxidizal)le and was biologically 

 inactive when tested on polyneuritic pigeons. Cautious reduction of thia- 

 mine pyrophosphate with activated hydrogen, however, gave a dihydro- 

 cocarboxylase that also was not autoxidizable but that was active in curing 

 polyneuritic pigeons. 



On the other hand Zima and Williams^^ and Zima et al.^^ oxidized the 

 sodium salt of thiamine with iodine and obtained a product which they 

 assumed was formed from two molecules of thiamine, in which the S — H 

 of the thiazole half of the molecule is transformed to S — S. Thus, it appeared 

 that the thiamine/thiamine disulfide should form a reduction-oxidation 

 system just as does cysteine/cystine or glutathione and its disulfide. 



Karrer and "\^iscontini,^^' '^ however, chemically synthesized the thia- 

 mine disulfide pj'rophosphate. This was combined with the apoenz3^me, the 

 alkali-washed yeast. The product was inactive with pyruvic acid. There- 

 fore the disulfide form of cocarboxylase is not the active coenzyme. Never- 

 theless, the disulfide may be active in the animal organism, but only by 

 preliminary reduction to thiamine itself. Similarly, Peters'^ found that the 

 disulfide is active only after reduction. But the fact that in vitro tissue prep- 

 arations are able to reduce the disulfide appears, in Peters' opinion, to 

 leave room for the suggestion of Williams and Zima that the disulfide may 

 play a part in the dehydrogenation. 



Barron and Lyman^^ showed that the thiamine pyrophosphate was more 

 resistant to oxidation and reduction than thiamine itself. They concluded 

 that the action of thiamine pyrophosphate as a component of enz.yme sys- 

 tems does not involve reversible oxidation and reduction. They were led 

 to postulate that the phosphorylated thiamine acts as the integral part of 

 the activating protein. After summarizing all the work that has been per- 

 formed until now, we must conclude that much more experimental work 



*2 F. Lipmann and G. Perlman, /. Am. Chem. Soc. 63, 2574 (1938). 



'' R. R. Williams, R. E. Waterman, J. C. Kuesztesj^ and E. R. Buchman, J. Am. 



Chem. Soc. 57, 536 (1935). 

 9^ P. Karrer, W. Graf, and J. Schrucki, Helv. Chim. Acta 28, 1523 (1945). 



95 (). Zima, and R. R. Williams, Ber. IZ, 941 (1940). 



96 O. Zima, K. Ritsert, and Th. Moll, Z. physiol. Chem. 267, 210 (1941). 

 " P. Karrer and M. Viscontini, Helv. Chim. Acta 29, 711 (1946). 



98 R. A. Peters, A^ture 158, 707 (1946). 



