HISTIDINE AND TYROSINE PHOSPHORYLATION IN PEA MITOCHONDRIA - EVIDENCEFOR PROTEIN-PHOSPHORYLATION IN RESPIRATORY REDOX SIGNALING

A 37 kDa protein in pea mitochondria was found to contain phosphorylat ed residues. Phosphorylation nas acid-labile but stable in alkali solu tion, a unique property of phosphorylation on histidine, indicating th at a signal transduction pathway with homology to bacterial two-compon ent systems might exist in plant mitochondria. We also describe the fi rst example of tyrosine phosphorylation in plant organelles and the fi rst indication of protein phosphorylation as part of a redox signallin g mechanism in mitochondria. Labelling of three proteins (28, 27 and 1 2 kDa) was found to be dependent on the redox state of the reaction me dium. Their phospho-groups were resistant to alkali as well as acid tr eatment and labelling was inhibited by the tyrosine kinase inhibitor g enistein.