II. CHEMISTRY 303 



OlluT iiivostij!;;itors had olttaiucd impuic preparations of (laviti. As early as LS?!), 

 A. W. lilyth isolated from whey a resinous preparation of a rcd-oraiiKe color whieh he 

 called "lactochroni." In 1025, H. Hleyer and (). Kallmann attempted the purification 

 of the yellow pigment of whey. In 1932, I. Banga and A. Szent-Gyorgyi obtained a 

 jiolden -yellow pigment from heart muscle, whose colored component they called 

 "cytoflav." In 1033, Ellinger and Koschara described impure, crystalline prepara- 

 tions of flavin ("lyochrome"), at the same time that the isolation of pure, crystallized 

 lactoflavin was published uiuUm- the authorship of Gyorgy, Kuhn, and Wagner- 

 Jauregg. The vitamin nature of the pigment was unknown before the investigations of 

 the latter authors. Shortly after, in 1933, L. E. Booher in the United States described 

 a concentrate from whey powder with the chemical and biological properties of 

 riboflavin. Soon other investigators followed with the isolation of riboflavin from 

 various natural sources. 



For the understanding of the biochemical function of riboflavin, the discovery of 

 the "yellow enzyme" by Warburg and Christian in 1932 was of extraordinary im- 

 portance. The same authors described lumiflavin, a photochemical degradation 

 product of riboflavin, which proved of great value for the elucidation of the chemical 

 structure of riboflavin (Kuhn, Rudy, Wagner Jauregg, and coworkers, 1933-34). 

 The synthesis of riboflavin by Kuhn and Weygand in Heidelberg and by Karrer and 

 his coworkers in Ziirich in 1934 finally confirmed the structural formula. 



A. ISOLATION 



Three factors mainly govern the possibihty of isolating riboflavin from 

 natural sources in a pure state and in good yield: (1) the concentration in 

 which the pigment occurs; (2) the amount and kind of accompanying sub- 

 stances; (3) the form (free or bound) in which the vitamin is present. 



1. The concentrations of riboflavin in different natural materials are 

 listed in a later section. In cases of low concentration, one will usually have 

 to dispense with the isolation and to confine oneself to the quantitative 

 determination according to either the vitamin test or one of the fluoro- 

 metric methods.^ 



2. Considerable difficulties in the isolation of riboflavin can be caused 

 by the presence of accompanying substances. As an example the liver might 

 be mentioned. Although this organ has a very high content of riboflavin, 

 the isolation of the crystallized substance was rather difficult and was per- 

 formed only one year after the preparation of riboflavin from other sources 

 had been described.^^- ^^^ 



3. Riboflavin occurs in its free, dialyzable form only, in the retina of the 

 eye, in whey, and in urine. In organs, tissues, and other living cells, ribo- 

 flavin is present, as riboflavin monophosphoric acid, and as riboflavin 

 adenine diimcleotide. The two phosphates account for practically all the 

 riboflavin present in rat kidneys, and 70 to 00% of the total ribofhnin in 



- P\>r recent developments of the fluorometric methods to determine vitamin IV.. in 



plants, see H. Roth, liiochem. Z. 320, 3.55 (1950). 

 ••■' \{. Kuhn and T. Wagner-Jauregg, Her. 67, 1770 (193Ji. 

 '•' r. Karrer, H. Salomon, and K. Schopp, Hclv. ('him. Acta 17, 419 (1934). 



