Degradation of stromal proteins in pea (Pisum sativum L) chloroplasts under oxidising conditions

Chloroplasts from pea leaves (Pisum sativum L.) were isolated to study the influence of activated oxygen species on stromal protein catabolism. Either lysed or intact chloroplasts were incubated in the light in the presence or absence of oxygen radical-generating systems. In lysed chloroplasts, phosphoglycolate phosphatase (EC 3.1.3.18), glutamine synthetase (EC 6.3.1.2) and the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) were cleaved when Fe, H2O2 and ascorbate were present in the incubation medium. In intact chloroplasts, stromal proteins were degraded when chloroplasts were exposed to light (45 mu mol m(-2) s(-1)) at 25 degrees C, High light (2700 mu mol m(-2) s(-1)) or the addition of methyl viologen to the incubation medium accelerated the degradation of glutamine synthetase, phosphoglycolate phosphatase and the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase and increased the content of carbonyl groups in stromal proteins. These results suggest that thr degradation of some stromal proteins is accelerated after exposure to free radicals of oxygen.