DEGRADATION OF ACTIVE-OXYGEN-MODIFIED RIBULOSE-1,5-BISPHOSPHATE CARBOXYLASE OXYGENASE BY CHLOROPLASTIC PROTEASES REQUIRES ATP-HYDROLYSIS/

Active oxygen (AO) species generated in plants under stress conditions trigger degradation of Rubisco (EC 4.1.1.39). To find out whether AO species activate proteases or make the protein susceptible to proteoly sis, purified and C-14-labelled Rubisco protein was incubated with str omal preparations obtained from barley (Hordeum vulgare L.) leaves. Th e protein was degraded into distinct fragments only after a treatment with AO. This result shows that AO-treated Rubisco has been modified t o become a substrate for stromal protease(s) and dismisses the possibi lity of protease activation. Upon degradation, distinct fragments accu mulated with time. The fragmentation pattern was indistinguishable fro m that obtained with intact chloroplasts subjected to oxidative condit ions (cf. M. Desimone et al., 1996, Plant Physiol 111. 789-796). Degra dation required ATP-hydrolysis, since AMP, ADP or non-hydrolysable ATP -analogs did not support proteolysis. The ClpP-deficient stromal prepa rations degraded AO-modified Rubisco, making the involvement of the Cl pC/P protease unlikely.