Protein phosphorylation in Rhodospirillum rubrum: Further characterization of the B873 kinase activity

Abstract

Protein phosphorylation of the B873 light-harvesting complexes in the phototrophic bacterium, Rhodospirillum rubrum G9, is an important means to regulate energy transduction. The B873 kinase activity is found in the water-soluble fraction and phosphorylates not only the α- and β-subunits but also a third, new component, Ω, which copurifies with the B873 complex. The B873 kinase is unaffected by the presence of cAMP but is weakly inhibited by ADP and AMP. Mg 2+ stimulates the kinase reaction but the transition metal ions Cu 2+ and Zn 2+ ellicit the most active phosphorylation. The B873 kinase also phosphorylates in vitro purified B873 light-harvesting complexes from R. rubrum. The extent of phosphorylation of the B873 complexes in intact chromatophores is dependent on the redox state of the quinone pool as well as of the cytochrome bc 1 complex. Fluorescence measurements of the B873 complexes of isolated chromatophores confirmed the functional significance of the phosphorylation events observed.