Protein Phosphorylation in Plant Mitochondria

Abstract

Protein kinase activity was detected in osmotically lysed mitochondria isolated from etiolated seedlings of corn [Zea mays cv. W64AN], pea [Pisum sativum cv Alaska], soybean [Glycine max cv. Hobbit], and wheat [Triticum aestivum cv. Brule], as well as from potato [Solanum tuberosum] tubers. Ther kinase(s) phosphorylated both endogenous polypeptides and exogenous, nonmitochondrial proteins when supplied with ATP and Mg2+. Eight to fifteen endogenous mitochondrial polypeptides were phosphorylated. The major mitochondrial polypeptide labeled in all species migrated during denaturing electrophoresis with an apparent monomeric molecular weight of 47,000. Incorporation of phosphate into endogenous proteins appeared to be biphasic, being most rapid during the first 1 to 2 minutes but slower thereafter. The kinase activity was greatest at neutral and alkaline pH values and utilized ATP with a Km of approximately 200 micromolar. The kinase was markedly inhibited by CaCl2 but was essentially unaffected by NaF, clamodulin, oligomycin, or cAMP. These data suggest tht plant mitocondrial protein phosphorylation may be similar to protein phosphorylation in animal mitochondria.