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Bioenergetic factors controlling in vitro phosphorylation of LHIα (B870) polypeptides in membranes isolated from Rhodobacter capsulatus
Authors:Norma L Pucheu  Norma L Kerber  Patricia Pardo  Matthias Brand  Gerhart Drews  A F García
Institution:Cátedra de Microbiología, Facultad de Agronomía (UBA), Ave. San Martín 4453, Capital Federal, Argentina Tel. 54-1-524-8061; Fax 54-1-523-4936 e-mail: garcia@fotgar.uba.ar, AR
Institut für Biologie 2, Mikrobiologie der Universit?t, Sch?nzlestrasse 1, D-79104 Freiburg, Germany, DE
Abstract:Membranes of Rhodobacter capsulatus strain U43 (pTX35) showed qualitatively very similar phosphorylation patterns under in vitro and in vivo conditions. In vitro, it was irrelevant whether the phosphate source was orthophosphate or ATP. Inhibitors of electron transport did not inhibit light-harvesting complex I (LHIα) (B870) polypeptide phosphorylation, except for o-phenanthroline, which was strongly inhibitory. Redox conditions regulated the amount of protein phosphorylated; external redox potentials between +200 and +300 mV promoted the reaction. Phosphorylation was inhibited by uncouplers such as carbonyl cyanide m-chlorophenyl hydrazone and nigericin plus valinomycin plus potassium ions. Inhibitors of the H+-ATPase were also inhibitory when the phosphate source was 32P]Pi or γ-32P]ATP. From these results, it was concluded that an operative reaction center, a coupled membrane, and external redox potentials higher than +200 mV are required for optimum LHIα phosphorylation. We also demonstrated that phosphorylation of LHIα polypeptide occurs before insertion into the membrane and that phosphate is preferentially incorporated into specific domains within the cytoplasmic membrane. Intracytoplasmic membranes, identified here as light membranes, were found to contain a dephosphorylated LHIα polypeptide. Received: 24 April 1995 / Accepted: 6 November 1995
Keywords:Protein phosphorylation  ATP-Pi exchange  Light-harvesting complexes  Reaction center  Photosynthesis  Photomorphogenesis  Membrane  growth  Polypeptide insertion  Phospho-amino esters
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