INVOLVEMENT OF UBIQUITIN IN PHOSPHOENOLPYRUVATE CARBOXYLASE DEGRADATION

Western immunoblot analysis of protein extracts prepared from epiderma l peels, whole leaves, and mesophyll protoplasts with ubiquitin and PE PCase antibodies indicated ubiquitinated PEPCase bands and degradation products only in crude extracts which have been obtained in the prese nce of the proteolysis inhibitors leupeptin and hemin. After ammonium sulfate precipitation and further purification, PEPCase forms were sta ble and not ubiquitinated. It is assumed, that only a certain part of PEPCase is degraded via the ubiquitin-dependent proteolysis.