THE VISUAL PIGMENTS 



observed). In these circumstances, the opsin is present in large excess 

 and the course of regeneration appears to be monomolecular, because 

 the concentration of opsin is only slightly reduced through combina- 



1 — r 



kinetics of rhodop^in synthesis: 



neore-fineneb •*■ opsin 

 (<*) (6) 



rhedopiin 



iO 



40 60 



Time — minuter 



^ — \ — V 



0.8 



-L0.4X 



I 



M 



».o 



BO 



40 



Fig. 5.7. The kinetics of the synthesis, in solution, of rhodopsin from 

 neo-TGi'mQUQi b and cattle opsin. Curve on left shows the rising extinc- 

 tion at 500 m^a as the synthesis proceeds. Straight line on right indicates 

 that the reaction follows a bimolecular course. 

 {Hubbard and Wald, 1952) 



tion with the active isomers present and is, therefore, effectively 

 constant throughout the reaction. 



THE STEREOCHEMICAL FORM OF RETINENEi IN BLEACHED 

 RHODOPSIN SOLUTIONS 



When a solution of rhodopsin is bleached at ordinary tempera- 

 tures, and then placed in darkness there is normally very little 

 regeneration of photosensitive pigment. This suggests that the 

 retinene or retinene-protein (indicator yellow) formed by bleaching 

 is not of the necessary spatial configuration required for synthesis. 



CHASE (1937) and chase and smith (1939) found that when 

 rhodopsin was bleached by light which included the short wavelength 

 region of the spectrum there was some regeneration of pigment in 

 darkness, but that if yellow Hght were used for bleaching there was 



146 



