title: Blue Light Induces Phosphorylation at Seryl Residues on a Pea (Pisum sativum L.) Plasma Membrane Protein.
abstract: We have partially characterized the blue-light-stimulated in vitro phosphorylation of a membrane protein from etiolated Pisum sativum L. stems. Properties of the response have implicated its involvement in signal transduction of phototropic stimuli (T.W. Short, W.R. Briggs [1990] Plant Physiol 92: 179-185; P. Reymond, T.W. Short, W.R. Briggs [1992] Proc Natl Acad Sci USA 89: 4718- 4721). Analysis of proteolysis products and phosphoamino acidanalysis indicate that the substrate protein is phosphorylated on multiple seryl residues. Kinetics of the in vitro reaction show phosphorylation to be complete within 2 to 5 min at 30[deg]C in either light-exposed or dark-control plasma membrane preparations, regardless of whether the membranes were first solubilized in Triton X-100. Nucleotide competition assays show the kinase to be ATP specific. The pH optimum covers a broad range with a maximum near 7.5. A wide array of salts inhibits the phosphorylation at high concentrations, but millimolar concentrations of Mg2+ are required to form Mg.ATP complexes for maximal activity, whereas excess free Mg2+ or Ca2+ are not required for the reaction.
authors.affiliation: University of California-Berkeley/United States Department of Agriculture Plant Gene Expression Center, 800 Buchanan Street, Albany, California 94710 (T.W.S.).
authors.forename: T. W.
authors.initials: TW
authors.lastname: Short
authors.forename: M.
authors.initials: M
authors.lastname: Porst
authors.forename: J.
authors.initials: J
authors.lastname: Palmer
authors.forename: E.
authors.initials: E
authors.lastname: Fernbach
authors.forename: W. R.
authors.initials: WR
authors.lastname: Briggs