Light-regulated permeability of rhodopsin:egg phosphatidylcholine recombinant membranes.

Abstract

Purified rhodopsin was incorporated into phospholipid bilayers of egg phosphatidylcholine to give recombinant membrane vesicles, which were examined by proton and phosphorus nuclear magnetic resonance spectroscopy. Increased rhodopsin content in the membranes appears to progressively inhibit the molecular motions of the methyl, methylene, and phosphate groups of the phospholipid molecules. This indicates that regions of the rhodopsin molecule interact in a manner that affects the phospholipids from the aqueous interface to the bilayer midline. In the dark, the recombinant vesicles were sealed to europium, manganese, or cobalt ions. Light exposure allowed rapid equilibration of Mn2+ and Co2+, and somewhat slower equilibration of Eu3+ across the membrane. Light changed the membrane permeability, and the gradient in chemica tential resulted in a net ion movement across the rhodopsin:phospholipid recombinant membrane. The results suggest rhodopsin is a transmembrane protein.

Functional reassembly of membrane proteins in planar lipid bilayers

“…Flash illumination, which bleached approximately 80 % of rhodopsin, released all the trapped 45 Ca+; (Hubbell et al 1977). These results were confirmed with NMR techniques where a light-induced permeability increase to Mn 2+ , Eu 2+ and Co 2+ was observed (O'Brien et al 19776). Therefore light induces the formation of a poorly selective permeability pathway in rhodopsin-phospholipid vesicles.…”

The dual role of rhodopsin in vision: light‐driven charge translocation and formation of long‐lived photoproducts

“…As to the light-induced rise of Ca 2+ permeability of a rhodopsin-containing membrane, it is apparently very rapid. In our experiments on photoreceptor discs incorporated into a collodion film [2], we not only confirmed observations on the light-dependent increase in disc membrane permeability [24,[42][43][44][45][46][47][48][49][50] but also revealed that such an effect requires < 50 ms. (A faster measurement is impossible because of a conductivity increase due to operation of rhodopsin as a photogenerator of much lower internal resistance than that of the disc membrane. )…”

Transient dichroism in photoreceptor membranes indicates that stable oligomers of rhodopsin do not form during excitation

“…It has long been proposed that the primary role of rhodopsin is to release an ionic transmitter (Ca"+) from disk membranes (1,2), presumably by acting as a lightactivated Ca"+ channel, and there is now strong evidence for both the release of Ca"+ from disk membranes and its transmitter role in vertebrate outer segments (3)(4)(5)(6). Moreover, purified rhodopsin has been shown to mediate changes in ion permeability for Ca"+ and H+ as well as other cations in recombinant phospholipid vesicles i-n response to light (7)(8)(9)(10) and Ca++ can be released from preloaded disk membrane vesicles (11) by photoexciting rhodopsin. If rhodopsin functions as a light-activated ion channel,' a fundamental question is whether a rhodopsin 'The possibility of a carrier mechanism cannot be ruled out, although the transmembrane structure of rhodopsin does not require it.…”