A New Class of Potential Mechanism-Based Suicide Inhibitors of Photosynthetic Activity
Inhibitors on the donor side of Photosystem II (PSII) in higher plants have been limited to an assortment of small amines (NH2OH, NH2NH2, NH3, etc.) and various derivatives of 2-anilino-thiophenes and phenylhydrazone derivatives which together form a group called the ADRY reagents. These compounds have all been shown to effectively disrupt the normal cyclization through the S-states of the Water-Oxidizing Complex (WOC), which is known to contain a special arrangement of four manganese ions. Identification of the proteins which bind these manganese ions and the specific amino acids which surround the site is still unknown. The reactivity of the first class of inhibitors at the manganese site is well documented, however, their usefulness in elucidating the protein environment surrounding the metal site has been limited. To approach this goal, we have developed a new class of inhibitors of the WOC which could react specifically with the manganese site to form a reactive species that is capable of covalently modifying the surrounding protein matrix in the active site. A similar approach has proven to be successful in identifying the binding site for Qb, the secondary electron acceptor, to be on the D1 subunit using photoaffinity labelling with azido[14C]atrazine, a herbicide which binds to the Qb site (1). By an analogous method, the location of the PSII electron donor, Z+, has also been proposed to be located on the Dl subunit, as shown by its photooxidation of 125I-(2).
KeywordsDonor Side PSII Membrane PSII Core Complex Carbene Intermediate Extrinsic Polypeptide
Unable to display preview. Download preview PDF.
- (4).Ghanotakis, D., Demetriou, D. and Yocum, C.F., Progress in Photosynthesis Research, Vol. 1, 1.5.681–1.5.684, J. Biggins, editor, Martinus Nijhoff Publ., 1987.Google Scholar
- (6).Kuwabara, T. and Murata, N., Plant Cell Physiol., 23, 533–539, 1982.Google Scholar
- (7).Encyclopedia of Electrochemistry of the Elements, XIII; Chp. 6, Bard, A.J., editor. Marcel Dekker, Inc., 1979.Google Scholar
- (8).Gilchrist, T. and Rees, C., Carbenes, Nitrenes, and Arynes, Appleton-Century-Crofts, 1969.Google Scholar
- (11).Babcock, G., Ghanotakis, D., Ke, B. and Diner, B., Biochim. Biophys. Acta, 723, 276–286, 1986.Google Scholar
- (13).Sivaraja, M. and Dismukes, G. C., Biochim. Biophys. Acta, in press.Google Scholar