Isotopic labelling of the polypeptide subunits of the isolated photosystemII reaction-centre complex of Chlamydomonas reinhardtii suggests an alpha beta heterodimeric structure for cytochrome b-559

The photosystem II reaction-centre (PSII RC) complex contains live polypept ides: D1, D2, PsbI and the alpha and beta subunits of cytochrome b-559. In order to determine their stoichiometry, we have isolated a PSII RC from a m utant of the green alga Chlamydomonas reinhardtii, lacking the photosystem I and chloroplast ATP-ase complexes, which has been grown in the presence o f [C-14] -acetate. The stoichiometry of the polypeptides is estimated by SD S-polyacrylamide electrophoresis followed by phosphorimage analysis of the gel. Our data suggest equimolar amounts of each polypeptide. Assuming the p resence of homogeneous PSII RC complexes, our results are consistent with a n alpha beta heterodimeric structure for cytochrome b-559. (C) 1999 Elsevie r Science S.A. All rights reserved.