Studies on the relation of the Mr 9000 phosphoprotein to cytochrome b-559 in spinach thylakoid membranes.
Cytochrome b-559 was purified from phosphorylated spinach chloroplast thylakoids after activation of kinase activity in the presence of [gamma-32P]ATP in order to determine whether the 9-kDa phosphoprotein in these membranes arises from phosphorylation of the cytochrome b-559. It was established in this work that the 9-kDa phosphoprotein, like the cytochrome b-559 polypeptide, is a PS II component, and that these two proteins migrate very similarly on denaturing gels. However, the initial 2% Triton-4 M urea membrane extract contains most of the cytochrome b-559 and little 32P. A substantially larger amount of stable 32P-labeled 9-kDa phosphoprotein fraction is found in the material that is insoluble in the 2% Triton-4 M urea. Furthermore, the ratio of 32P:heme in cytochrome b-559 purified in the presence of protease inhibitors from phosphorylated membranes was on the order of 1% of that expected if cytochrome b-559 were the sole source of the radiolabel seen in the 9-kDa band. The differential extraction properties of the 32P-labeled 9-kDa phosphoprotein and cytochrome b-559, and the stoichiometry of 32P:heme in the purified cytochrome appear to exclude the cytochrome as a candidate for the 9-kDa phosphoprotein.
D002736:Chloroplasts / Q000378:metabolism*; D003573:Cytochrome b Group / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D007425:Intracellular Membranes / Q000378:metabolism*; D007700:Kinetics; D008027:Light; D008565:Membrane Proteins / Q000302:isolation & purification / Q000378:metabolism*; D008970:Molecular Weight; D010750:Phosphoproteins / Q000302:isolation & purification / Q000378:metabolism*; D010785:Photophosphorylation; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D010944:Plants / Q000378:metabolism*
D003573:Cytochrome b Group; D008565:Membrane Proteins; D010750:Phosphoproteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; C042085:thylakoid membrane phosphoprotein, plant; C019313:cytochrome b559