INTERACTION OF GUANOSINE 5'-TRIPHOSPHATE BINDING-PROTEIN GQ FROM SEPIA-OFFICINALIS WITH ILLUMINATED RHODOPSIN BOUND TO CONCANAVALIN-A

The heterotrimeric guanosine 5'-triphosphate (GTP)-binding protein Gq was suggested to couple the light receptor rhodopsin with the effector phospholipase C in visual cells of invertebrates. We indirectly linke d Gq from Sepia officinalis to a concanavalin A-sepharose column via r hodopsin. Rhodopsin had been solubilized previously with 10 mM n-dodec yl-beta-maltoside from the purified photosensory membrane under illumi nation. All three subunits of the Gq were released almost pure by elut ion with 100 mu M GTP. The alpha and beta subunits were identified by specific antipeptide antisera. The alpha subunit has a relative molecu lar mass of 46 kDa, and the beta subunit of 35 kDa. The gamma subunit corresponds to a 9 kDa polypeptide owing to the molecular mass, which is similar to the G(gamma) subunit of squid. The use of specific antib odies shows that neither actin nor G-protein related to transducin wer e in the fractions eluted with GTP or alpha-methyl mannoside. We demon strate that all three subunits of Gq were associated with rhodopsin of invertebrates. Such use of a lectin column might be useful for furthe r investigations of the interaction of rhodopsin and Gq.