Some properties of solubilized human rhodopsin.

This investigation involved an examination of some properties of solubilized human rhodopsin. In confirmation of previous work, the spectral maximum was found to be at 493 nm at temperatures 5-10 degrees C below 37.5 degrees C. An increase in temperature to 37.5 degrees C produced only a minor shift of 2-4 nm toward the blue. The opsin displayed the classic and typical stereospecificity of vertebrate visual pigments, regenerating a pigment at 493 nm with 11-cis retinal and an isopigment at 483 nm with 9-cis retinal. No regeneration occurred with either all-trans or 13-cis retinal. The chromophoric photosensitivity of human rhodopsin and of its 11-cis regenerated pigment was found to be the same at 13.2 X 10(-17) cm2; that of the isopigment, at 4.5 X 10(-17) cm2. The long-lived photoproduct of human rhodopsin at 475 nm (metarhodopsin-III) was found to be especially interesting because of its protracted growth following a brief (20 sec) light exposure of the pigment and because of its long decay time even at 27 degrees C and higher. This property (growth and decay of metarhodopsin-III) was studied at temperatures ranging from 1.9 to 37.5 degrees C. Though NH2OH (4.6 X 10(-3) M) was found to speed the decay of metarhodopsin-III, it did not prevent its presence during decay for minutes after the 20-sec bleach. It is clear that the human metarhodopsin-III is indeed a long-lived intermediate of bleaching and evidence from the literature, which is cited, suggests that this product persists for significant periods of time in the retinas of mammals, including that of man. This fact suggests the possible physiological role of metarhodopsin-III in some aspects of vertebrate vision.