Isolation and partial characterization of a membrane bound protein kinase from mitochondria of Saccaromyces cerevisiae

Saccharomyces cerevisiae mitochondria, isolated by enzymatic lysis of the cell wall and purified by gradient centrifugation are able to phosphorylate serine residues of exogenous phosphoproteins in the presence of added [γ32P] ATP. Most of the protein kinase activity is bound to the mitochondrial membranes from which it can be partially solubilized by 0.7 M NaCl. The solubilized protein kinase, whose M.W. is approximately 30,000, has been partially purified by Phosphocellulose chromatography: it displays its activity toward "acidic" phosphoproteins (αs2-casein>αs1-casein = phosvitin > β-casein) while it does not phosphorylate histones even in the presence of cAMP. The enzyme requires Mg2+, which cannot be replaced by Mn2+, and is strongly inhibited by inorganic Phosphate. © 1978.