Ovine rhodopsin may be cleaved in situ by Staphylococcus aureus V8 proteinase into two membrane-bound fragments designated V8-L (27 000 mol.wt.) and V8-S (12 000 mol.wt.). After purification of the proteolysed complex by affinity chromatography in detergent using concanavalin A immobilized on Sepharose 4B, the two polypeptide fragments may be separated by gel-permeation chromatography on Sephadex LH-60. Digestion of the N-terminal-derived V8-L fragment with CNBr in 70% (v/v) trifluoroacetic acid resulted in a peptide mixture that could be fractionated by procedures involving gel-permeation chromatography in organic and aqueous solvents and the use of differential solubility. The complete or partial sequences of all ten peptides are reported.
The organization of rhodopsin in the photoreceptor membrane of sheep rod outer segments was investigated by using a variety of bifunctional reagents. Of the nine reagents used, seven gave oligomeric opsin species, whereas two, copper phenanthroline and dithiobisphenyl azide, failed to cross-link the protein. In general, the cross-linked species obtained showed diminishing yields from dimer to tetramer, together with some higher-molecular-weight aggregates. It is proposed that the patterns of cross-linking arise as a result of collision complexes and best describe a monomeric organization for native rhodopsin. No significant differences between the patterns obtained with dark-adapted bleached or regenerated protein states were observed. This interpretation is discussed in relation to the postulated mechanism of action of rhodopsin.
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