title: Effects of calcium on light-activated GTP-binding proteins in squid photoreceptor membranes.
abstract: 1. At least two distinct G-proteins are activated by light in squid photoreceptor membranes, a 45,000 mol. wt cholera toxin substrate and a 40,000 mol. wt pertussis toxin substrate. 2. The light-stimulated GTPase activity is partially inhibited by pretreatment with either toxin and abolished by treatment with both toxins. 3. At 24 degrees C, a free calcium ion concentration of 1 microM inhibits GTPase activity of both toxin substrates and ADP ribosylation by pertussis toxin. 4. This calcium sensitivity of squid G-proteins may be important in interpretation of experimental results on the phosphoinositide or other signalling pathways in squid visual transduction.
authors.affiliation: Department of Zoology, University of Oxford, UK.
authors.forename: J M
authors.initials: JM
authors.lastname: Fyles
authors.forename: J
authors.initials: J
authors.lastname: Baverstock
authors.forename: K
authors.initials: K
authors.lastname: Baer
authors.forename: H R
authors.initials: HR
authors.lastname: Saibil
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002772:Cholera Toxin / Q000378:metabolism / Q000494:pharmacology; D049832:Decapodiformes / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000037:antagonists & inhibitors / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism* / Q000528:radiation effects; D008027:Light; D008970:Molecular Weight; D037342:Pertussis Toxin; D010786:Photoreceptor Cells / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D010566:Virulence Factors, Bordetella / Q000378:metabolism / Q000494:pharmacology
chemical_list: D010566:Virulence Factors, Bordetella; D000246:Adenosine Diphosphate Ribose; D002772:Cholera Toxin; D037342:Pertussis Toxin; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D002118:Calcium