CHEMICAL CROSS-LINKING STUDIES OF EXTRINSIC PROTEINS IN CYANOBACTERIAL PHOTOSYSTEM-II

Chemical crosslinking with a zero-length crosslinker, 1-ethyl-3-(3-dim ethylaminopropyl) carbodimide hydrochloride, was applied to a cyanobac terial photosystem II complex retaining three extrinsic proteins, the 33 kDa manganese-stabilizing protein, cytochrome (cyt) c-550 and the 1 2 kDa protein. Three major crosslinked products were obtained in addit ion to the crosslinked product between the extrinsic 33 kDa and the in trinsic CP47 proteins. They were identified to be: cyt c-550-12 kDa; c yt c-550-12 kDa-33 kDa; D2-cyt c-550-12 kDa. These results indicate th at the three extrinsic proteins are closely located with each other in cyanobacterial PSII, supporting the previous proposal that, like the 33 kDa protein, cyt c-550 and the 12 kDa protein are associated with P SII at the lumenal. side of thylakoids. The results also suggested tha t the D2 reaction center protein provides a direct binding site for th e extrinsic cyt c-550.