72 



VITAMINS A AND CAROTENES 



which occurs to some degree in the isolated retina and even in solution ; and 

 a slower "neogenesis" from colorless precursors, which Kiihne believed to 

 occur only in the living eye and to require the cooperation of the pigment 

 epithelium.^* These processes can now be identified with the synthesis of 

 rhodopsin from the yellow retinene, and from the colorless vitamin A. 

 Hecht et al}^ and Chase and Smith"*^ confirmed Kiihne's observation that 



o.** - 



0.3 - 



■♦' O.Z 

 X 



(U 



OJ - 



Frog- 

 rhodops in -protein 

 ■h rei inene I 



Ligh-t 



\ 1 1 1 r 



9-20-49 



Difference sp&cfrum 

 A-B 



ZO 



40 



60 400 



mi nuies 



v\/ave1eng-th~mjj 



Fig. 18. The synthesis of rhodopsin from retinene and opsin. A solution of frog 

 opsin was mixed with retinene (10 y per milliliter), and this mixture was incubated 

 in the dark at room temperature. The measurements at the left follow the rise in 

 extinction at 500 mix as rhodopsin is synthesized. At A the product was exposed to 

 daylight for 20 minutes; it bleached to B. The difference in the absorption spectrum 

 before and after this bleaching {A-B) is shown at the right. It has the maximum at 

 aljout 498 niju characteristic of regenerated rhodopsin (From G. Wald and P. K. 

 Brown.^^) 



rhodopsin regenerates slightly in solutions which are bleached — to retinene 

 and opsin — ^and replaced in the dark. Their usual regenerations were in the 

 neighborhood of 5 to 10%; the largest reported was 15%. 



Recently we found that, when rhodopsin solutions are supplemented with 



«W. Kiihne, in L. Hermann: Handbuch der Physiologie, Vol. 3, Part 1, p. 321. 



F. C. W. Vogel, Leipzig, 1879. 

 " S. Hecht, A. M. Chase, S. Shlaer, and C. Haig, Science 84, 331 (1936). 

 '"> A. M. Chase and Emil L. Smith, /. Gen. Physiol. 23, 21 (1939-1940). 

 ^6 G. Wald and P. K. Brown, Proc. Natl. Acad. Sci. U. S. 36, 84 (1950). 



