THIAMINE 685 



reduction. Early investigation of this possibility showed that thiamine, 

 under suitable conditions, took up one mole of hydrogen when reduced 

 catalytically or by means of sodium hydrosulfite, 19 but the reduction 

 product was biologically inactive. On the other hand dihydrothiamine 

 pyrophosphate, prepared by catalytic hydrogenation, was found to be as 

 active as thiamine pyrophosphate. 19 However, none of these reduction 

 products was autoxidizable. 



Later investigations showed that under conditions as mild as those 

 prevailing in growing tissues, thiamine 20 and thiamine pyrophosphate 21 

 (cocarboxylase) can be oxidized either by dilute hydrogen peroxide at 

 pH 7.5 or by iodine in alkaline solution to form the corresponding di- 

 sulfide derivative without loss of vitamin Bi activity; this conversion 

 involves the opening of the thiazole ring, and the disulfide may be repre- 

 sented by the following formula: 



CH 2 CH 3 CH 3 CH 2 



CH 3 



-C C N 



I 



J-NH 2 CH0 C-S-S-C CHO HtN J^ 



CH 2 GH 2 



I I 



CH 2 OH CH2OH 



-CH 3 



The disulfide can be reduced by cysteine or glutathione. 22 More re- 

 cently it has been shown that thiamine pyrophosphate disulfide is inactive 

 in the yeast carboxylase enzyme system, 23 and although fermenting yeast 

 is able to reduce the cocarboxylase disulfide, it appears that the disulfide 

 form may not be involved in the biological functioning of thiamine. 



More vigorous oxidation of thiamine yields thiochrome, 24 a yellow 

 compound with intense blue fluorescence; this compound is biologically 

 inactive, except for a few microorganisms. 25 



H 2 

 fVV-C-CH 3 



! II 



nvt C C— CH 2 CH 2 OH 



thiochrome 



In general, it appears that animals require the complete thiamine 

 molecule, but plants and many microorganisms can utilize a mixture of 

 the pyrimidine and thiazole components for the synthesis of vitamin Bi. 

 Some organisms require only one of the components, and others are cap- 



