Light-induced proteolysis of stromal proteins in pea (Pisum sativum L) chloroplasts: requirement for intact organelles

In intact chloroplasts isolated from mature pea leaves (Pision sativum L.), the catabolism of ribulose-1,5-bisphosphate carboxylase/oxygenase as well as several other stromal proteins was strongly accelerated by illumination. However, when proteolysis was compared in intact and lysed chloroplasts this rapid, light-induced degradation of stromal proteins was markedly reduced following lysis of the organelles. Varying the pH of the incubation medium in a physiologically relevant range or adding adequate concentrations of ATP or Mg2+ could not restore rapid protein breakdown in lysed chloroplasts. Using an approach combining fluorography, Coomassie-staining and immunoblotting, the stability of several stromal proteins in intact and lysed organelles could be monitored simultaneously in the same chloroplast preparation. Evidence is presented that the light-induced proteolysis is a genuine intraplastidial process. (C) 1997 Elsevier Science Ireland Ltd.