Presence of rhodopsin-like proteins in sorghum bicolor and Pisum sativum

Antiserum raised against squid (Loligo forbesi) rhodopsin cross-reacted wit h proteins from microsomal and plasma membranes isolated from Sorghum bicol or and Pisum sativum In S. bicolor the main crossreacting protein (SbR) pre sented a molecular mass of 38 kDa. SbR appeared to be more abundant in meso cotyl microsomal membranes than in leaf or root membranes. SbR showed simil arities to G-protein coupled receptors (GPCRs) in that it required a high d etergent concentration for extraction and exhibited diffuse antibody staini ng on blots similar to that of squid rhodopsin. In P. sativum hypocotyl mem branes the strongest immunological signal corresponded to a 35 kDa polypept ide (PsR) that was shown to be enriched in plasma membranes. A P. sativum g lycoprotein bearing the same Mr and membrane association behaviour as PsR c ould be purified by Con A affinity chromatography and elution with alpha me thyl manoside. The chromatographic fractions containing the glycoprotein we re shown to possess high and specific GTP gamma S binding activity, indicat ing association to G-proteins. The glycoprotein showed weak cross-reaction to anti-rhodopsin serum. N-terminal sequencing of the glycoprotein did not show high homology to other proteins in the databases but indicated a likel y amphipathic character.