448 THIAMINE 



among the bacteria, yeast, and fungi investigated, that the growth of those 

 requiring intact thiamine is inhibited by a much lower concentration of 

 pyrithiamine than those which respond to one or both components, whereas 

 those with no thiamine requirements were not appreciably inhibited. In 

 Neurospora there seemed to be no definite correlation between capacity for 

 synthesis of thiamine and its components and the degree of inhibition of 

 pyrithiamine. 



Several authors have demonstrated a favorable influence of light on the 

 biosynthesis of thiamine. Bonner and Greene^*^ found, for example, that the 

 thiamine content of pea plants kept in the dark did not increase, whereas 

 in the light this content rose rapidly. 



VII. Estimation 



B. C. P. JANSEN 



A. PHYSICAL 



Thiamine may be estimated by its absorption in the ultraviolet at 265 

 mju. This method has been used in the laboratory of von Muralt^ in Bern 

 by Liithy- for measuring the thiamine content of nerve fibers. 



To distinguish the thiamine from other substances (nuclein components) 

 absorbing at 265 mju, the absorption may be measured before and after 

 destroying the thiamine by ferricyanide. 



B. CHEMICAL 



Barger et al? showed that thiamine on oxidation with ferricyanide in 

 alkaline solution is transformed into thiochrome, see facing page. 



This thiochrome is characterized by a strong blue fluorescence. Jansen 

 found that in a very strong alkaline solution and with a suitable quantity 

 of ferricyanide the transformation is practically quantitative. The thio- 

 chrome is extracted from the aqueous solution by isobutanol. Thus the 

 fluorescence of the thiochrome, which is accurately measured in a fluoro- 

 meter, may be used as a yardstick for the thiamine.^ 



It could be expected that this method is not only sensitive but also spe- 

 cific for use in biological fluids and extracts. Bouman^ found, however, that 



10 J. Bonner and J. Greene, Botan. Gaz. 100, 226 (1938). 



1 A. von Muralt, Die Signalubermittlung in Nerven. Birkhauser, Basel, 1946. 

 ^n. Luthy, Helv. Physiol. Acta 4, C20 (1946). 

 3G. Barger, F. Bergel, and A. R. Todd, Nature 136, 259 (1935). 

 * B. C. P. Jansen, Rec. trav. chim. 55, 1046 (1936). 

 5 J. Bouman, Z. Vitaminforsch. 19, 386 (1948). 



I 



