The photochemical and macromolecular aspects of vision

Structures of the Visual Chromophores and Related Pigments: A Conformational Basis of Visual Excitation

“…The presence of different conformers in rhodopsin would be expected to broaden the absorption spectrum, since individual conformers will possess different degrees of conjugation and, hence, different spectral characteristics. However, this mechanism alone does not explain the red shift observed for rhodopsin, relative to retinal (20).…”

“…In the absence of detailed structural information concerning the conformation of the chromophore and its environment in rhodopsin, one might use the present knowledge of possible conformations for the chromophore, and of the types of interactions that have been observed between ligands and proteins in x-ray crystallographic studies, to construct a model for the active site of rhodopsin. In view of the markedly different Xmax values for rhodopsin and for the free chromophore in homopolar solvents (20), one may suggest that while the chromophore is likely to interact in similar ways with ligands of comparable ;hydrophobicity, the presence of specific polar groups in suitable positions in opsin may be responsible for the red shift.…”

The minimum latency of the a‐wave

“…Hagins concluded that the thermal fading of 'A' could not rate limit the excitatory process, and although the latent period of the a-wave found in this paper is some two orders smaller, at body temperature the same conclusion must obviously still apply. But the decay of metarhodopsin I slows some 10-to 15-fold for a 100 C drop in temperature (Hagins, 1956) and other estimates are even higher (hundredfold- Matthews, Hubbard, Brown& Wald (1963); see also Abrahamson & Ostroy, 1967). Thus the use of intense flashes at reduced temperature might produce a situation where the latent period was dependent upon the thermal fading of metarhodopsin I.…”

“…Other intermediates need not be considered. Those preceding metarhodopsin I have such short half lives (even at 00 C) that for present purposes they may be considered to decay instantaneously (see Abrahamson & Ostroy, 1967). The later intermediates decay so slowly that they may be considered stable.…”

Selective photoinduced Ca2+ diffusion in rhodopsin–lipid bilayers: an internal transmitter hypothesis

“…Many detergents have been used for these purposes such as digitonin (56)(57)(58)(59)(60), Emulphogene BC (61), cholic acid (62), and Triton X-100 (63,64). We have chosen Triton X-100 for its removability and for the ease of following its removal by the absorbance decrease at 275 nm.…”