Dimer to monomer conversion of the cytochrome b(6)f complex - Causes and consequences

The molecular weight of the cytochrome b(6)f complex purified from Chlamydomonas reinhardtii thylakoid membranes has been determined by combining velocity sedimentation measurements, molecular sieving analyses, and determination of its lipid and detergent content. The complex in its enzymatically active form is a dimer. Upon incubation in detergent solution, it converts irreversibly into an inactive, monomeric form that has lost the Rieske iron-sulfur protein, the b(6)f-associated chlorophyll, and, under certain conditions, the small 32-residue subunit PetL. The results are consistent with the view that the dimer is the predominant form of the b(6)f in situ while the monomer observed in detergent solution is a breakdown product. Indirect observations suggest that subunit PetL plays a role in stabilizing the dimeric state. Delipidation is shown to be a critical factor in detergent-induced monomerization.