ISOMERISM AND THE VISUAL PIGMENTS 



not test the homogeneity of cyanopsin. Moreover in view of the 

 number of 'passengers' in the experiment, viz. chicken rhodopsin, 

 chicken iodopsin not bleached by the original exposure to deep red 



300 



400 



700 



500 600 



Wavelength in nn|i 



Fig. 5.10. The difference spectrum of cyanopsin, a photosensitive 



pigment formed from the opsin of chicken iodopsin and an isomer of 



retinenea icisi). 



(After Wald, Brown and Smith, 1953) 



light, and any pigment regenerated from the products of the original 

 bleaching, the purity of cyanopsin may be questioned. 



WALD, BROWN and SMITH (1953) consider that cyanopsin would 

 probably occur in any retina which contains vitamin Ag or retinencg 

 and cone opsin. They attribute the fact that cyanopsin, as such, has 

 not been demonstrated in a retinal extract to the common practice of 

 making extracts by red Hght— which would, of course bleach any 



153 



