NA-ATPASE FROM THE PLASMA-MEMBRANE OF THE MARINE ALGA TETRASELMIS (PLATYMONAS) VIRIDIS FORMS A PHOSPHORYLATED INTERMEDIATE()

Plasma membranes isolated from the marine unicellular alga alga Tetras elmis (Platymonas) viridis were phosphorylated by [gamma-P-32]ATP, and membrane proteins mere then analyzed by PAGE in SDS, under acidic con ditions. Three radioactive components with apparent molecular masses o f 100 kDa, 76 kDa, and 26 kDa were detected. The phosphorylation of on e of them, the 100 kDa polypeptide, was specifically stimulated by Na. Vanadate almost completely inhibited the Na+-mediated phosphorylatio n of the peptide. The phosphate bound to this peptide underwent rapid turnover and was discharged by hydroxylamine. The 100 kDa phosphopepti de was sensitive to ADP. The conclusion is drawn that the 100 kDa phos phopeptide is a phosphorylated intermediate of the Na+-transporting AT Pase in the T. viridis plasma membrane. (C) 1998 Federation of Europea n Biochemical Societies.