Tw. Short et al., BLUE-LIGHT INDUCES PHOSPHORYLATION AT SERYL RESIDUES ON A PEA (PISUM-SATIVUM L) PLASMA-MEMBRANE PROTEIN, Plant physiology, 104(4), 1994, pp. 1317-1324
We have partially characterized the blue-light-stimulated in vitro pho
sphorylation of a membrane protein from etiolated Pisum sativum L. ste
ms. Properties of the response have implicated its involvement in sign
al 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 produc
ts and phosphoamino acid analysis 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
degrees C in either light-exposed or dark-control plasma membrane prep
arations, regardless of whether the membranes were first solubilized i
n Triton X-100. Nucleotide competition assays show the kinase to be AT
P specific. The pH optimum covers a broad range with a maximum near 7.
5. A wide array of salts inhibits the phosphorylation at high concentr
ations, but millimolar concentrations of Mg2+ are required to form Mg.
ATP complexes for maximal activity, whereas excess free Mg2+ Or Ca2+ a
re not required for the reaction.