THE PHYSICAL CHEMISTRY OF VISUAL PURPLE 



supposed that the transient orange chromophores underwent a 

 dismutation reaction; half of them losing an electron to give indica- 

 tor yellow and the other half gaining an electron to yield iso- 

 rhodopsin. 



COLLINS and morton assumed that the dismutation of transient 

 orange to iso-rhodopsin and indicator yellow must also have taken 



0-35 



0-30 — 



§0-25 



in 

 6 



c 



0-10 



0-05 



I I I I I I I I I I I I I I I 1 I I 1 I i I I 



rr 



t I I I t I I I I I I I I I I I I I I I I I I I I 



400 500 600 



Wavelength in mju 



Fig. 3.8. The partial bleaching of a frog's visual purple solution at 

 20°C. Curve 1 density spectrum of unbleached solution; curve 2, after 

 1 hr bleaching with light of dominant wavelength 580 m^^; curve 3, 

 after a further 2 hr, curve 4, after a further 17 hr. Note the isosbestic 

 point and absence of evidence for iso-rhodopsin (cf. Fig. 3.7). 



place in the experiments of dartnall, goodeve and lythgoe, 

 with consequent reduction of the overall quantum yield to one half. 

 But when a visual purple solution is bleached under similar condi- 

 tions to those in the experiments of dartnall et al, no iso-rhodop- 

 sin is formed (dartnall, unpubhshed). For example, in Fig. 3.8, 

 curve 1 is the original density spectrum of a visual purple solution 



81 



