NEAREST-NEIGHBOR ANALYSIS OF D1 AND D2 SUBUNITS IN THE PHOTOSYSTEM-IIREACTION-CENTER USING A BIFUNCTIONAL CROSS-LINKER, HEXAMETHYLENE DIISOCYANATE

A cross-linked product between the D1 and D2 subunits was generated by treating isolated spinach PS II reaction center with a bifunctional c ross-linker, 1,6-hexamethylene diisocyanate. To obtain information on the contact site(s) between D1 and D2 proteins, the cross-linked produ ct was cleaved by CNBr, the resultant fragments were separated using a reverse-phase HPLC, and then the partial sequence of the cross-linked polypeptide fragments were determined. By comparing the results with the deduced amino acid sequence of the D1 and D2 proteins from spinach , it is concluded that the C-terminal domains of the D1 subunit (D308- A334) and that of the D2 subunit (Y297-L353) are in close proximity.