title: ADP-ribosylation of thylakoid membrane polypeptides by cholera toxin is correlated with inhibition of thylakoid GTPase activity and protein phosphorylation.
abstract: Incubation of pea thylakoid membranes with [32P]-NAD+ in the presence of cholera toxin resulted in the [32P]-ADP-ribosylation of a 60 kDa thylakoid membrane polypeptide. When ATP was included in the incubation mixture, a 29 kDa polypeptide was also labelled. In the absence of electron transfer cofactors or inhibitors, the extent of labelling depended on whether the membranes were preincubated in the light or dark and also on the developmental stage of the leaves used for thylakoid isolation. Irrespective of the latter, the strongest labelling was observed when DCMU was present in the light. After pretreatment of the thylakoid membranes with cholera toxin plus NAD+ under the same conditions, light-stimulated GTPase activity and protein phosphorylation were inhibited. The extent of inhibition for both processes appeared to be correlated with the amount of [32P]-ADP-ribosylation found when [32P]-NAD+ was included in the pretreatment mixture. The data presented are fully consistent with the 60 and 29 kDa polypeptides functioning as thylakoid membrane associated guanine nucleotide binding regulatory proteins.
authors.affiliation: Department of Biochemistry, University of Leeds, U.K.
authors.forename: P A
authors.initials: PA
authors.lastname: Millner
authors.forename: P S
authors.initials: PS
authors.lastname: Robinson
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000502:physiology; D002736:Chloroplasts / Q000378:metabolism*; D002772:Cholera Toxin / Q000494:pharmacology; D007887:Fabaceae; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000187:drug effects / Q000502:physiology; D008027:Light; D008565:Membrane Proteins / Q000378:metabolism*; D009243:NAD / Q000502:physiology; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D010766:Phosphorylation; D010770:Phosphotransferases / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism*; D010946:Plants, Medicinal
chemical_list: D008565:Membrane Proteins; D010940:Plant Proteins; D009243:NAD; D000246:Adenosine Diphosphate Ribose; D000255:Adenosine Triphosphate; D002772:Cholera Toxin; D010770:Phosphotransferases; D010744:Phosphoric Monoester Hydrolases; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins