392 VITAMIN K GROUP 



tra of vitamins Ki and K2 prepared by Doisy and coworkers. Each vitamin 

 showed maxima at 243, 249, 260, and 270 m/x and a broad absorption in 

 the region of 310 and 340. The Ej^. at 249 m/x was 540 for Ki and 305 

 for K2. These extinction coefficients were higher than those reported pre- 

 viously.^^- 2" The purified vitamin Ki in hexane solution exposed to daylight 

 decreased in absorption so fast that in 15 minutes the extinction coefficient 

 at 249 was about 420 and at 1 hour about 350. The other maxima also 



2-]\Iethyl-3-hydroxy- 2-IVIethyl- 1 ,4-naphthoquinone 



1,4-naphthoqumone Menadione 



Phthiocol 



CH3 

 CH2CH=C(CH2)3CH(CH2)3CH(CH2),CHCH3 



CH3 CH3 CH3 CH3 



2-]\Iethyl-3-phytyl-l,4-naphthoquinone 

 Vitamin Ki 



"^ 







CH3 

 CH2(CH=C-CH2-CHo),CH-C-CH3 



CH3 CH3 



2-]\Iethyl-3-difarnesyl-l,4-naphthoquinone 

 Vitamin K2 



Fig. 1. Forms of vitamin K. 



dropped similarly. Ewing et al.^^ have further studied the absorption spec- 

 trum of vitamin Ki, again finding evidence of rapid drops in absorption 

 as the vitamin in hexane solution was exposed to ultraviolet light. A new 

 value for the extinction coefficient at 249 mn was given at 435 ± 5. The 

 literature was thoroughly discussed. More recently, the extinction co- 

 efficient for K2 at 249 m/x has been given as 520, which is considerably 

 higher than the earlier values.^^ It seems evident, therefore, that unless 

 determined almost instantly after the vitamin was exposed to light the 

 absorption at 249 m/x would have decreased by an indeterminate amount 

 and could hardly be used as a criterion of purity. 



31 D. T. Ewing, F. S. Tomkins, and O. Kamm, J. Biol. Chem. 147, 233 (1943). 



