Incorporation of Rhodopsin Proteolipid into Bilayer Membranes

Abstract

RHODOPSIN constitutes over 80% of the membrane-bound protein in the outer segment of rod photoreceptors^1,2. Absorption of light by rhodopsin leads to large changes in the ionic current of the receptor cell³: excitation of a single rhodopsin molecule transiently (∼1 s) stops about 10⁷ Na ions from flowing across the plasma membrane of the outer segment^4,5. The mechanism by which the excited rhodopsin molecule achieves such large reduction in ionic flux is not understood, partly because natural rhodopsin-containing membranes amenable to the experimental methods required to investigate the transport properties of rhodopsin have not been successfully prepared. As an alternative to natural membranes, attempts to form model membranes which incorporate the properties of the photoreceptor have been made. Takagi et al.⁶ and Fesenko et al.⁷ have reported the incorporation of ultrasonicated fragments of rod outer segments into model membranes. In this study we report the successful incorporation of native, purified rhodopsin into bilayer membranes. This should make possible the investigation of the mechanism by which rhodopsin molecules act in the rod photoreceptor.