LOW-MOLECULAR-WEIGHT SUBUNITS ASSOCIATED WITH THE CYTOCHROME B6F COMPLEXES FROM SPINACH AND CHLAMYDOMONAS-REINHARDTII

Cytochrome b6f complexes, prepared from spinach and Chlamydomonas thyl akoids, have been examined for their content of low molecular weight s ubunits. The spinach complex contains two prominent low molecular weig ht subunits of 3.7 and 4.1 kD while a single prominent component of 4. 5 kD was present in the Chlamydomonas complex. An estimation of the re lative stoichiometry of these subunits suggests several are present at levels approximating one copy per cytochrome complex. The low molecul ar weight subunits were purified by reversed phase HPLC and N-terminal sequences obtained. Both the spinach and Chlamydomonas cytochrome com plexes contain a subunit that is identified as the previously characte rized petG gene product (4.8 kD in spinach and 4.1 kD in Chlamydomonas ). A second subunit (3.8 kD in spinach and 3.7 kD in Chlamydomonas) ap pears to be homologous in the two complexes and is likely to be a nucl ear gene product. The possible presence of other low molecular weight subunits in these complexes is also considered.