Photosynthetic Water Oxidation in Cytochromeb559Mutants Containing a Disrupted Heme-binding Pocket

Francisco Morais, Kristina Kühn, David H. Stewart, James Barber, Gary W. Brudvig, Peter J. Nixon
2001 Journal of Biological Chemistry  
The role of cytochrome b 559 in photosynthetic oxygen evolution has been investigated in three chloroplast mutants of Chlamydomonas reinhardtii, in which one of the two histidine axial ligands to the heme, provided by the ␣ subunit, has been replaced by the residues methionine, tyrosine, and glutamine. Photosystem two complexes functional for oxygen evolution could be assembled in the methionine and tyrosine mutants up to ϳ15% of wild type levels, whereas no complexes with oxygen evolution
more » ... ity could be detected in the glutamine mutant. PSII supercomplexes isolated from the tyrosine and methionine mutants were as active as wild type in terms of light-saturated rates of oxygen evolution but in contrast to wild type contained no bound heme despite the presence of the ␣ subunit. Oxygen evolution in the tyrosine and methionine mutants was, however, more sensitive to photoinactivation than the WT. Overall, these data establish unambiguously that a redox role for the heme of cytochrome b 559 is not required for photosynthetic oxygen evolution. Instead, our data provide new evidence of a role for cytochrome b 559 in the protection of the photosystem two complex in vivo.
doi:10.1074/jbc.m103935200 pmid:11390403 fatcat:djbb3pr2j5dsrlpa62szhktopi