THE VISUAL PIGMENTS 



cyanopsin present. They showed that the absorption spectrum of 

 cyanopsin bears a close resemblance to the photopic sensitivity 

 curves of the tortoise {testudo graced) and the tench {tinea tinea) as 

 found by granit (1941) using a micro-electrode technique, and 

 consider that the retinae of both these animals contain retinencg and 

 Gone opsin, the ingredients of cyanopsin. 



Finally, if instead of c/^i retinencg, c/^g-retinencg (a different eis 

 isomer of retinenca) is incubated with chicken cone opsin as in the 

 experiment described above, a different pigment having Amax at 

 575 mjLi and which wald calls wo-cyanopsin, is formed. 



SUMMARY 



The preceding description of the visual pigment situation, as seen 

 by WALD and his colleagues, is summarized in the following table 

 (wald, 1953a, wald, brown and smith, 1953). 



Composition of visual photopigments and of their cis-trans 

 artifacts, the iso pigments 

 The visual pigments : 



The scheme of this table gives an impression of universality which 

 is not yet warranted. For example it implies that *rhodopsin' — 

 whatever its source — is derived from weo-retinenci b and scotopsin. 

 In fact, this has been estabUshed only for cattle rhodopsin. Other 

 retinenci isomers — inactive as regards cattle opsin — might well be 

 active with opsins of other animals. Similarly, the data given for 

 *porphyropsin* were obtained *using opsin from a fresh-water fish* 

 (wald, 1953a). The extrapolation of this result to embrace all such 



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