THE VISUAL PIGMENTS 



Visual Purple (Amax = 497-503 mjn) 

 (Rhodopsin) 



Photochemical 



LUMI-RHODOPSIN (Amax = C. 490 m//) 



ISO-RHODOPSIN 



(Amax = 487-493 m^) 



Thermal 



V^e./N^^c^/ MeTA-RHODOPSIN (Amax = C. 480 m/u) 



(Transient orange) 



Thermal (and photochemical?) 

 (in presence of water) 



y pH 



Acid Indicator ^ Alkaline Indicator 



Yellow Yellow 



(Amax == 440 mju) (Amax = 365 mju) 



Thermal 



Thermal and Enzymic 

 (via retinene?) 



Retinene + Protein 

 (Amax = 385 mju) 



Thermal and Enzymic (pH 5*5-8) 



Vitamin A + Protein 



(Amax = 328 m/x) 



Scheme showing the products which may be formed when 



visual purple is bleached 



The scheme, which embodies the work of a number of authors, 

 enables us to forecast the products of bleaching of visual purple 

 under a wide variety of conditions. 



At very low temperatures, or in the dry state, the bleaching of 

 visual purple proceeds only as far as lumi- or meta-rhodopsin and 

 the regeneration of rhodopsin or of iso-rhodopsin either do not 

 occur or are immeasurably slow. 



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