THE STRUCTURE OF VISUAL PURPLE (RHODOPSIN) 



similar shapes, that for astacene is roughly twice the height of that 

 for visual purple. Since astacene has a 'double vitamin A' structure 

 this suggests that the visual purple chromophore contains only one 

 molecule of vitamin A. 



90000 



80000 



t 70000 

 i> 



£60000 

 o 



^50000 

 o 



"? 40000 



j; 30000 

 m 



2 20000 

 10000 



330 



400 



450 500 



Wavelength in mp 



550 



600 



Fig. 4.2. Comparison of the density spectra of astacene (in pyridine) 

 with that of visual purple (in digitonin solution). The dotted curve gives 

 the density spectrum of visual purple equated at 500 mfx to that for 



astacene. 



In a recent molecular weight determination (see Chap. 3, p. 94), 

 HUBBARD (1954) has shown that the molecule of cattle visual purple 

 contains a single chromophore based on one C20 unit. 



THE RELATIONSHIP BETWEEN RETINENEj 

 AND VITAMIN A^ 



A considerable step forward was made when it was found that 

 retinenci is the aldehyde of vitamin A^ 



CHO 



retinenci (vitamin A^ aldehyde) 



MORTON (1944) had come to this conclusion purely from a con- 

 sideration of absorption spectra. The problem was how to prove it, 



103 



