Abstract
In this study, we found random degradation of a number of subunit components in oxygen-evolving photosystem II particles (crude PSII) isolated from a centric diatom, Chaetoceros gracilis, at room temperature in the dark, which were not observed in PSIIs from other organisms, suggesting the existence of diatom-specific proteases. The degradation was remarkably inhibited by EDTA, PMSF or Cu ion, implying the presence of metalloproteases and serine proteases. The degradation was stimulated with an increase in temperature and optimal at 40-45 degrees celsius but depressed above 50 degrees celsius. To examine the localization of these proteases, the crude PSII was solubilized with 1% Triton X-100 and then applied to DEAE-toyopearl column, which resulted in pure PSII containing no FCP. The significant degradation found in the crude PSII was not observed in the pure PSII. This indicates that proteases in the crude PSII were separated from PSII components during column procedures.
