| In Loligo pealei, activation of phototransduction involves conversion of rhodopsin to metarhodopsin, which activates Gq and the phospholipase C pathway. Inactivation involves rhodopsin phosphorylation and arrestin binding to metarhodopsin. Squid rhodopsin kinase (SQRK) can phosphorylate arrestin, in Ca2+-dependent manner, in addition to rhodopsin; a dual role unique among GRK proteins.; This study reports the purification of squid visual arrestin. By dark-adaptation, light-sensitive rhabdomeric membranes were prepared, facilitating partial characterization of arrestin-membrane interaction. Light-prepared membranes lack light-sensitivity due to photobleaching and perhaps a lack of retinoid photoisomerase activity.; Light-dependent arrestin binding to rhodopsin was demonstrated in vitro. Membrane association was also stimulated by Ca2+ and inhibited by IP6. Ca2+-dependent interactions at the membrane apart from those with SQRK may contribute to Ca2+-dependent activation of arrestin as a SQRK substrate. Increases in arrestin phosphorylation were observed in the presence of conditions favoring membrane association, including Ca2+, light: and GTPgammaS. |
