Evidence that the amino-terminus of the 33 kDa extrinsic protein is required for binding to the Photosystem II complex.

Chymotrypsin and Staphylococcus aureus (strain V8) proteinase eliminated sixteen and eighteen amino acid residues, respectively, from the amino-terminal side of the extrinsic 33 kDa protein of the oxygen-evolving Photosystem II (PS II) complex of spinach. The carboxy-terminus of the resultant large fragments was found to be identical with that of the intact protein. Neither fragment could rebind to PS II membranes depleted of all the extrinsic proteins. Circular dichroism spectroscopy did not reveal any major conformational change within the two fragments. These results suggest that the amino-terminal region of the 33 kDa protein contains a domain essential for binding to the PS II complex.