SMALL GTP-BINDING PROTEINS OF SQUID PHOTORECEPTOR - INTERACTION WITH PHOTOACTIVATED RHODOPSIN

Squid photoreceptor membranes contain several small GTP-binding protei ns (22-27 kDa) in addition to heterotrimeric G-proteins. In addition, these membranes contain several proteins which can be ADP-ribosylated by exoenzyme C-3 from Clostridium botulinum (C-3). These proteins are similar but not identical to C-3 substrates from bovine rod outer segm ents. It is shown that substrates of C-3 in squid photoreceptor intera ct with rhodopsin in a light-dependent manner. These data suggest invo lvement of small GTP-binding proteins in phototransduction processes i n invertebrates.