THE STRUCTURE OF VISUAL PURPLE (RHODOPSIN) 



a 1 M solution of freshly neutralized hydroxylamine was added, 'to 

 prevent further regeneration and to remove fortuitous retinenej 

 complexes.' The density spectrum before and after exposure to light 

 was then measured. The change gave the difference spectrum of the 

 regenerated rhodopsin. A control bleaching of another sample of 

 the original solution to which hydroxylamine had been added gave 



T 



Fig. 4.5. The regeneration of cattle visual purple in bleached solutions 

 containing added retinenei. Regeneration time 2-2^ hr, temperature, 



24-27°C. 

 (Wald and Brown, 1952) 



the difference spectrum of the original rhodopsin. From these 



results the percentage regeneration was calculated. 



The results are given by the pH-activity curve in Fig. 4.5. This 



shows that the optimum condition for regeneration was at pH 6. 



Above pH 7 and below pH 4-5, however, little regeneration occurred. 



+ 

 Since — NHg groups exist mainly as the non-reactive — NHg ions at 



pH's below 6-7 whereas — SH groups do not appreciably ionize at 



pH's below 8-9, v^ald and brow^n (1952) considered that 'one 



can conclude from these measurements alone that the synthesis of 



rhodopsin is optimal at pH's which are disadvantageous for the 



117 



