Association of the 33-kDa polypeptide with the 43-kDa component in photosystem II particles

AbstractThe organization of polypeptides and Mn atoms in the oxygen-evolution system was studied by analyzing the effects of protease treatment on photosystem (PS) II particles from spinach chloroplasts. Hydrolysis of the 47- and 43-kDa polypeptides of the PS II core complex had similar profiles of dependence on trypsin concentration in the treatment of control PS II particles and NaCl-washed particles, which were devoid of the peripheral 24- and 18-kDa polypeptides. In CaCl2-washed particles, which were depleted of the 33-kDa polypeptide besides the 24- and 18-kDa polypeptides, the 43-kDa polypeptide was much more sensitive to trypsin than the 47-kDa polypeptide. Chymotrypsin treatment gave similar results. These findings suggest that the 33-kDa polypeptide is associated to the 43-kDa polypeptide and shields it from tryptic attack. Changes of the amount of Mn in the PS II and salt-washed particles on protease treatment indicated a heterogeneity of binding sites of Mn in the PS II particle