MODULATION OF ENDOGENOUS PROTEIN-PHOSPHORYLATION IN PLANT-MITOCHONDRIA BY RESPIRATORY SUBSTRATES

Purified mitochondria from potato (Solanum tuberosum L. cv. Bintje) tubers were incubated with [gamma-P-32]-ATP, respiratory substrates and various effectors. The total incorporation of P-32 into proteins was measured and the phosphoprotein pattern investigated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and autoradiography. Total incorporation was strongly reduced (by 70-80%) by the respiratory substrates, succinate, pyruvate and NADH. The half-maximal inhibition was at 0.03, 0.3, and 0.3 mM, respectively. The labelling of the major phosphoproteins of 40 and 42 kDa (probably both the alpha-subunit of the pyruvate dehydrogenase, EC 1.2.4.1) as well as of minor polypeptides of 26-33 kDa was reduced. A concomittant increase in the labelling of the 14 and 16 kDa bands occurred in the presence of succinate in fall but this increase could not be detected in late winter. The reduction in total labelling caused by NADH and succinate was unaffected by changes in the membrane potential (e.g. addition of uncouplers) or by inhibition of electron transport (e.g. by KCN). Malonate inhibition of succinate oxidation reversed the effects of succinate on labelling. The mechanism(s) by which respiratory substrates might affect protein kinase activity is discussed.