Studies on the relation of the Mr 9000 phosphoprotein to cytochrome b-559 in spinach thylakoid membranes

• Published in: Archives of biochemistry and biophysics Vol. 233; no. 1; pp. 72 - 79
• Main Authors: Widger, William R., Farchaus, Joseph W., Cramer, William A., Dilley, Richard A.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15.08.1984
• Subjects: Chloroplasts - metabolism; Cytochrome b Group - metabolism; Electrophoresis, Polyacrylamide Gel; Intracellular Membranes - metabolism; Kinetics; Light; Membrane Proteins - isolation & purification; Membrane Proteins - metabolism; Molecular Weight; Phosphoproteins - isolation & purification; Phosphoproteins - metabolism; Photophosphorylation; Photosystem II Protein Complex; plant biochemistry; plant physiology; Plant Proteins; Plants - metabolism
• ISSN: 0003-9861; 1096-0384
• DOI: 10.1016/0003-9861(84)90602-7

Cytochrome b-559 was purified from phosphorylated spinach chloroplast thylakoids after activation of kinase activity in the presence of [γ- 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.