Isolation and characterization of a supramolecular complex of subunit iii of the atp-synthase from chloroplasts

In SDS gels of purified, highly active ATP-synthase from chloroplasts, CF₀F₁, a protein band was detected at an apparent m olecular weight of 100 kDa. This protein was isolated on a preparative SDS gel. The 100 kD a protein can be dissociated at increased tem perature or increased incubation time into an 8 kDa protein, which isidentical with the subunit III of CF₀(DCCD-binding protein or proteolipid). This implies that the 100 kDa band is a stable supramolecular com plex containing at least 12 copies of subunit III. Electron micrographs reveal a diam eter of 6.3 nm and a mem brane spanning length of 6.1 nm. We assume that this supramolecular complex represents a stablenative substructure of CF₀F₁.