THE HOMOGENEITY OF VISUAL PIGMENT SOLUTIONS 



their respective ^max, the sums being scaled to 100. The data are 

 only approximate; considerable fluctuations were observed in 

 different extracts made from the same species. 



The photoproducts of these pigments had Amax (estimated from 

 the lower portions of the difference spectra) as hsted below. 



Now retinenej absorbs maximally at 380 m/n and retinencg in the 

 405-410 m/Li region. This suggests that all the pigments found by the 

 partial bleaching technique are based either on retinenej or on 

 retinencg. To this extent, the results are consistent with wald's 

 findings (Chap. 2). Moreover, since the tench is often found in salt 

 water, the presence of a retinenej pigment (467) in this fish is, perhaps, 

 not surprising. Likewise, the euryhaline rainbow trout possesses 

 both a retinenci (508) and a retinenca (533) pigment. The only 

 unexpected result, therefore, is that for the bleak which has a retinenci 

 pigment (508) in addition to two retinencg pigments (533 and 550), 

 even though it is a fresh-water fish. This exception recalls the con- 

 verse case of the marine tautog (Chap. 2, p. 36) which has a pre- 

 dominantly vitamin Ag retina (wald, 1939a). 



Although the number of species so far examined by the partial 

 bleaching method is too small to justify any generalizations, it is 

 noteworthy that four out of five of the fish possess a pigment with 

 -^max at 533 m/Li, and only one (the carp) a pigment with Amax close to 

 that assigned by wald to 'porphyropsin' (522 m^). 



It is also evident that the visual pigment situation is more complex 

 than envisaged by wald (Chap. 5). If, for example, we regard the 

 five pigments 467, 508, 523, 533 and 550 as rod pigments then, 

 according to the classification on page 151, the protein moiety is, in 

 each case, *scotopsin.' Now the photoproducts obtained on bleach- 

 ing the pigments suggest that 467 and 508 are retinenci pigments and 

 hence should involve the specific isomer Azeo-retinenci b. Similarly, 

 pigments 523, 533 and 550 are based on retinencg, specifically cisi- 

 retinencg. Thus pigments 467 and 508 would both be classified as 

 'Azeo-retinencj b — scotopsin,* the identical composition accorded 

 (p. 154) to *rhodopsin' with Amax at 500 m/z. The pigments 523, 533 



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