THE VISUAL PIGMENTS 



retinene at 360 mju is 28,200 while that of alkaline indicator yellow is 

 50,000. If X is the concentration of retinene at a time / after bleaching 

 and y, that of indicator yellow, then the final concentration of 

 retinene will he x -\- y. Thus using the values at 360 m^ in Fig. 4.4 



(Curve A) 28,200jc + 50,000^ + / = 0-676 

 where / is absorption due to impurities and 



(Curve B) 28,200(x + y) + i = 0-543. 

 By subtraction, 



j(50,000- 28,000) = 0-133, 



whence j^; = 6-1 x 10"^ molar, i.e. 40 per cent of the potential 

 retinene (15-2 x 10~^). In another similar experiment y, the initial 

 indicator yellow concentration, was found to be 49 per cent of the 

 potential retinene. 



The hydrolysis of alkahne indicator yellow to free retinene and 

 protein (Fig. 4.4) is, like the hydrolysis of retinene methyhmine, a 

 monomolecular reaction but with a shorter half period, namely 

 9 min. Consequently, since 5-10 min elapsed between the beginning 

 of irradiation and the first density measurement at 360 mu, the initial 

 concentration of indicator yellow must have been a good deal higher 

 than 40-49 per cent of the potential retinene. In fact, immediately 

 after bleaching, all the retinene could have been in the form of 

 indicator yellow. 



VIEWS OF THE HARVARD SCHOOL ON THE 



STRUCTURE OF RHODOPSIN 



(VISUAL PURPLE) 



INDICATOR YELLOW 



In the preceding arguments concerning the structure of visual 

 purple (rhodopsin), indicator yellow has occupied a key position. 

 Recently the Harvard school (wald and his colleagues) have made 

 tentative observations on the structure of rhodopsin, and in doing so 

 have denied the relevance of indicator yellow. Before describing the 

 experiments on which they base their proposals for the rhodopsin 

 structure, it is necessary, therefore, to study their views on indicator 

 yellow. 



In a recent paper, wald and hubbard (1949) wrote *the retinenej- 

 protein which results from bleaching rhodopsin in solution is almost 

 colourless when alkahne and bright yellow when acid (chase, 1936). 



114 



