Photosynthetic electron transport in genetically altered photosystem II reaction centers of chloroplasts

Robin A. Roffey, John H. Golbeck, C. Russ Hille, Richard T. Sayre

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Abstract

Using a cotransformation system to identify chloroplast transformants in Chlamydomonas reinhardtii, we converted histidine-195 of the photosystem II reaction center D1 protein to a tyrosine residue. The mutants were characterized by a reduced quantum efficiency for photosynthetic oxygen evolution, which varied in a pH-dependent manner, a reduced capacity to oxidize artificial donors to photosystem II, and P680+ reduction kinetics (microsecond) that were essentially similar to wild type. In addition, a dark-stable radical was detected by ESR in mutant photosystem II particles but not in wild-type particles. This radical was similar in g value and lineshape to chlorophyll or carotenoid cations but could have arisen from a tyrosine-195 cation. The ability of the photosystem II trap (P680+) to oxidize tyrosine residues suggests that the mutant tyrosine residue could be used as a redox-sensitive probe to investigate the environment around the photosystem II trap.

Original languageEnglish (US)
Pages (from-to)9122-9126
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume88
Issue number20
DOIs
Publication statusPublished - Oct 15 1991

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