414 VITAMIN K GROUP 



absorption has been reported''^ (Fig. 3). As already mentioned, the absorp- 

 tion of these vitamins deteriorates rapidly on exposure to ultraviolet light. 

 Vitamin K can also be determined polarographically.*^' ^^ These physical 

 methods have been used only for relatively pure concentrates. Oxidation- 

 reduction methods have also been described/^- ^^ but they seem to be sub- 

 ject to much interference from other non-vitamin K substances. 



Numerous color reactions would be expected from a compound of the 

 naphthoquinone structure. Vitamin Ki gives a strong transient blue color 

 reaction with sodium ethylate, which fades to a more permanent red- 

 brown stage. This color reaction may apparently be expected only from 

 vitamins Ki and Ko, which have a double bond between the /S- and 7-carbon 

 atoms in the side chain, or from similar naphthoquinone derivatives.^^- ^^ 

 The more stable red-brown end stage of the reaction has a roughly quanti- 

 tative relation to the activities of concentrates.^^ It was stated that the 

 end-stage color was due to phthiocol.^^ However, the principal pigment pro- 

 duced in this reaction possessed an analysis and molecular weight indicating 

 that it was a derivative of vitamin Ki.^* A colorimetric assay based upon 

 the reaction of 2 , 3-substituted 1 , 4-naphthoquinones with sodium diethyl 

 dithiocarbamate has been reported. ^^ 



Colorimetric methods for 2-methyl-l ,4-naphthoquinone have excited in- 

 terest because of the wide use of this compound in vitamin K-active phar- 

 maceutical preparations. There have been used such color developers as 

 dichlorophenolindophenol,^^ dinitrophenylhydrazine,"- ^* and ethyl cyano- 

 acetate.^^ A specific color test for 4-amino-2-methyl-l-naphthol was de- 

 scribed."'' The reaction with aniline has been used for determination of 

 methyl naphthoquinone in blood and tissues."^ 



^6 D. T. Ewing, F. S. Tomkins, and O. Kamm, /. Biol. Chem. 147, 233 (1943). 



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« H. Onrust and B. Wostman, Rec. trav. chim. 69, 1208 (1950). 



4s G. V. Scudi and R. P. Buhs, J. Biol. Chem. 141, 451 (1941) ; J. Biol. Chem. 143, 665 



(1942). 

 ^0 N. R. Trenner and F. A. Bacher, J. Biol. Chem. 137, 745 (1941). 

 " L. F. Fieser, W. P. Campbell, and E. M. Fry, J. Am. Chem. Soc. 61, 2206 (1939). 

 " P. Karrer, Helv. Chim. Acta 22, 1146 (1939). 



S3 H. J. Almquist and A. A. Klose, /. Am. Chem. Soc. 61, 1610 (1939). 

 " H. J. Almquist and A. A. Klose, J. Biol. Chem. 130, 791 (1939). 

 " F. Irreverre and M. X. Sullivan, Science 94, 497 (1941). 

 S6 W. Bosecke and W. Laves, Biochem. Z. 314, 285 (1943). 

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