Similarities between G-proteins in visual cells of Sepia and cattle

In contrast to antisera against native transducin a polyclonal antiserum raised against heat-denatured bovine transducin crossreacts with the G-protein from Sepia visual cells. This antiserum recognizes a 44 kDa (G alpha) and a 36 kDa (G beta) protein band from Sepia photosensory membrane preparation. Furthermore we purified the antibody-binding G-protein from Sepia by binding it to light-activated rhodopsin of Sepia and GTP-induced extraction, similar to the purification of bovine transducin. This G-protein is probably involved in the phototransduction process. The purified Sepia G-protein did bind to vertebrate photosensoric membrane upon illumination, but was not eluted by GTP-containing buffer solution. After extensive bleaching, the G-protein became soluble.