Abstract
At high temperatures, the photosystem II reaction center D1 protein is cleaved into a 23kDa and a 10kDa fragments. Since the cleavage seems to occur at the DE-loop of the D1 protein, it is likely that the mechanism of the cleavage is the same as that in the 'primary cleavage' of the D1 protein during acceptor-side photoinhibition. In this work, we compared the heat-stimulated cleavage and degradation of the D1 protein with those of the acceptor-side photoinhibition in detail.
The results with protease inhibitors show that an extrinsic serine-type endopeptidase is associated with the heat-induced primary cleavage of the D1 protein, and an intrinsic protease is responsible for the secondary degradation of the 23kDa fragment. These results suggest that heat-induced proteolysis of the D1 is actually very similar to the proteolysis in the acceptor-side photoinhibition of photosystem II.
