Identification of a proteolipid oligomer as a constituent part of CF0, the proton channel of the chloroplast ATP synthase

摘要

>We studied the action of the photophosphorylation inhibitor, N,N′-dicyclohexylcarbodiimide (DCCD) on the channel portion (CF₀) of the chloroplast ATP synthase (CF₀CF₁). We found that the target for binding of [14C]DCCD was an oligomer of the small proteolipid-subunit (subunit III) of CF₀. We treated thylakoids with low concentrations of DCCD, sufficient to inhibit photophosphorylation. The 14C-labelled inhibitor was found on polyacrylamide gels in a position corresponding to an apparent molecular mass of 50 kDa. This band comprised a homooligomer of proteolipid subunits of CF₀. At higher concentrations of DCCD, it fell apart into proteolipid monomers. This dissociation was prevented by the presence of venturicidin, another CF₀ inhibitor acting on the proteolipid subunit, during the incubation with DCCD. The existence of such an oligomeric substructure in CF₀ is discussed in the light of diverging structural models for the proton channel of F₀F₁-type ATPases.