682 VII. VITAMINS A 



{Salvelinus fontinalis) , the rainbow trout (Salmo irideus), and the king or 

 qiiinnat salmon (Oncorhyncus tschaivylscha), have all been shown to follow 

 this pattern. In the case of the so-called catadromoiis fishes such as the 

 American "fresh-water" eel (Anguilla rostrata) and the killifish (Fundulus 

 heteroclitus) , which are fresh-water fishes but which spawn in salt water, 

 the retinas hkewise contain both rhodopsin and porphyropsin ; however, in 

 line with the salt-water varieties of fishes, the chief pigment gives rise to 

 retinenei and vitamin Ai. Some anadromous fishes such as the white 

 perch {Morone americana) and the alewife (Pomolohus pseudoharengus) 

 contain exclusively the porphyropsin (vitamin A2) system.^^'^* 



Among the amphibia, the common newt {Triturus viridescens) follows 

 the pattern of the anadromous fishes and possesses only porphyropsin.**^ 

 The frog (Rana spp.), on the other hand, has only the typical rhodopsin 

 system. Since Wald*^ considers the retinal use of vitamin A2 as an ex- 

 tremely ancient one, the variation in composition of the retinal pigments in 

 two such closely related species of amphibia is difficult to explain. 



Rhodopsin has been shown to be the photosensitive compound in the eyes 

 of such birds as the owP and the chicken.*^ In the case of the chicken, it 

 has been demonstrated that the filter pigments in the retina also contain 

 astaxanthin,^^ a mixture of xanthophylls, and an unidentified carotenoid 

 resembling sarcinene, which is a pigment related to the air-borne coccus 

 Sarcina lutea.^^ Astacene is found in the retina only in the case of the 

 chicken, and appears to be synthesized, since it is absent from the embry- 

 onic retina and does not occur in the yolk.^^ 



The retinas of rats, rabbits, cattle, sheep, and pigs,***'^^ as well as of the 

 monkey, cat, and dog,"" and also of man,*^*^'^^ possess the rhodopsin-vitamin 

 Ai system. The vitamin A-i-porphyropsin system can replace the usual 

 rhodopsin system in the retina of the rat when vitamin A2 is administered 

 over a 12- week period."^ 



The interrelations of the types of vitamins A and carotenoids of impor- 

 tance in retinal vision are represented diagrammatically in Figure 1 . 



Although the vitamins A are of such fundamental importance in vision, 

 their content in the retina may actually contribute only an extremely small 



«8 G. Wald, J. Gen. Physiol., 25, 235-245 (1941-1'.»42). 

 88 G. Wald, Biol. Sympos., 7, 43-71 (1942). 



^ E. Kottgen and G. Ahelsdorff, Z. Psijchol. Flu/siol. Sinnesorgane, 12, 161-184 

 (1896). 



" R. Kuhn, J. Steue, and X. A. S0rensen, Bet:, 72, 1688-1701 (1939). 

 ^^ G. Wald and H. Zussman, J. Biol. Chem., 122, 449-460 (1938). 

 S3 G. Wald, J. Gen. Physiol, 18, 905-915 (1934-1935). 

 s^ G. Wald, J. Gen. Physiol., 21, 795-832 (1937-1938). 



85 A. Konig and E. Kottgen, Sitzber. kgl. preuss. Akad. Wiss., 1894, J, 577-598. 



86 E. M. Shantz, N. D. Embree, H. Carpenter, and J. H. Wills, Jr., ,/. Biol. Chem., 163, 

 455-464 (1946). 



