THE HOMOGENEITY OF VISUAL PIGMENT SOLUTIONS 



bleak. These had Amax (after allowing for the i)min/max ratios — see 

 Fig. 2.6) ranging from 533 to 521 mju. This variation was found to 

 arise from differences in the relative proportions of the pigments 510, 

 533 and 550, and was largely caused by wide fluctuations in the 

 amount of pigment 550. This was the least 'robust' pigment as 

 judged by thermal stabiHty. Thus the close resemblance between the 



100 



I I 1 I I I 1 i 



450 500 550 



Wavelengch in mfi 



Fig. 6.8. Density spectra of the three photosensitive pigments in the 

 bleak retina, scaled to the proportions in which they occurred in the 

 extract of Fig. 6.6. +, pigment 510; O, pigment 533; •, pigment 550. 

 The dotted curve is the sum of these three curves brought, for compari- 

 son, to the same maximum (100) as that for pigment 533. 

 {Dartnall, 1955) 



pike and bleak data (Fig. 6.6) was a coincidence: if the data for the 

 extract with Amax = 521 m/z had been chosen, a similarly close com- 

 parison could have been made with carp extracts (visual pigment 523). 



COMPARISON BETWEEN DIFFERENCE SPECTRA OF THE VISUAL 

 PIGMENTS 



In Fig. 6.9, the difference spectra of pigments 467, 502 (visual 

 purple), 533 and 562 (iodopsin) are shown on a uniform scale of 

 wavelengths. The main feature brought out by this comparison i§ 



175 



