RIBOFLAVINE 



after hydrolysis in lo % trichloroacetic acid solution it is converted 

 into the monophosphate which has the same fluorescence as ribo- 

 flavine.^6" 



Physical Methods 



J. J. Lingane and O. L. Davis *' described a method of assaying 

 riboflavine polarographically. Riboflavine is reduced very readily at 

 the dropping mercury electrode, the optimal pH being 7-2. The 

 potential at the dropping electrode is — 0-47 volt and the diffusion 

 current is proportional to the concentration of riboflavine over the 

 range 2 to 50 p.p.m. Aneurine and nicotinic acid can also be esti- 

 mated polarographically and, in fact, the three substances can be 

 estimated simultaneously in the same solution, the resulting polaro- 

 gram exhibiting separate and well-defined waves for each substance. 

 Such a simultaneous assay is best carried out in unbuffered potassium 

 chloride solution as the base solution ; the potential of riboflavine is 

 then — 0*35 volt. 



The oxidation-reduction potential of riboflavine was first measured 

 by R. Kuhn and G. Moruzzi.^^ The shape of the titration curve 

 depended on the pK and, according to K. G. Stern, *^ the slope of the 

 curve at _^H values between 6-o and 12-4 corresponded to a two-electron 

 system, and between 4-0 and i-o to a one-electron system whilst at 

 0-4, two maxima appeared, indicating a two-stage process. R. Kuhn 

 and R. Strobele ^^ isolated three coloured intermediates — verdo-, 

 chloro-, and rhodo-flavine — in the conversion of riboflavine to leuco- 

 riboflavine (see page 199). 



References to Section 7 



1. H. von Euler and M. Malmberg, Z. physiol. Chem., 1937, 250, 



158. 



2. M. M. El Sadr, T. F. Macrae and C. E. Work, Biochem. J., 1940, 



34, 601. 



3. J. R. Wagner, A. E. Axelrod, M. A. Lipton and C. A. Elvehjem, 



/. Biol. Chem., 1940, 136, 357. 



4. M. F. Clarke, M. Lechycka and C. A. Cook, /. Nutrition, 1940, 20, 



133- 



5. H. R. Street, ibid., 1941, 22, 399. 



6. T. H. Jukes, ibid., 1937, 14, 223. 



7. E. E. Snell and F. M. Strong, Ind. Eng. Chem., Anal. Ed., 1939, 



11. 346. 



8. E. C. Barton-Wright, Nature, 1942, 149, 696 ; E. C. Barton- Wright 



and R. G. Booth, Biochem. J., 1943, 37, 25. 



9. R. D. Greene and A. Black, /. Amer. Pharm. Assoc, 1943, 32, 217. 

 10. M. Landy and D. M. Dicken, /. Lab. Clin. Med., 1942, 27, 1086. 



162 



