STRUCTURAL-CHANGES IN THE LUMIRHODOPSIN-TO-METARHODOPSIN-I CONVERSIONOF AIR-DRIED BOVINE RHODOPSIN

Structural changes during the photochemical reactions of unhydrated ai r-dried films of bovine rhodopsin in rod outer segments were examined by visible and Fourier transform infrared (FTIR) spectroscopy at 200, 240, and 280 K. These films exhibited conversion from a lumirhodopsin state to a metarhodopsin I state with a time constant of 13.5 min at 2 80 K, but did not form metarhodopsin II at all, as observed earlier fo r digitonin-extracted rhodopsin in dry gelatin films [Wald, Durell, an d St. George (1950) Science 111, 179-181]. Lumirhodopsin which was sta ble in the dry film was very similar to normal lumirhodopsin. The meta rhodopsin I-like state retained properties characteristic of lumirhodo psin in regard to a twisted structure between the C-14-H and the Schif f base of the chromophore, and perturbation around Glu122, although th e C-C stretch frequencies of the chromophore were identical with those of metarhodopsin I. Thus, under dry conditions some of the structural changes that lead to metarhodopsin I are partially inhibited. These d efects could result in stable lumirhodopsin and the failure to form me tarhodopsin II, which is in equilibrium with metarhodopsin I.