Immunological evidence for the presence of latent Ca2 dependent ATPase and carboxydismutase on the thylakoid surface.

Antibodies were prepared against carboxydismutase and latent Ca2® dependent ATPase (coupling factor) purified from Nicotiana tabacum. The antibodies against carboxydismutase inhi­ bit the enzymatic activity of the purified protein, while those against coupling factor inhibit the Ca2© dependent ATPase activity of the protein as well as the photophosphorylation of the chloro­ plasts. The antisera against these two proteins agglutinate the isolated lamellar systems of chloro­ plasts. The lamellar systems after repeated washes with ethylene diamine tetra-acetic acid loose their capacity to agglutinate with the antibodies. So treated lamellar systems regain their capacity to agglutinate when preincubated with purified coupling factor and carboxydismutase. It is con­ cluded that coupling factor and carboxydismutase molecules are present on the outer surface of the thylakoids. The antisera against the proteins isolated from Nicotiana show cross reactions with preparations of Antirrhinum. Coupling factor and carboxydismutase are non-uniformly distributed on the surface of thylakoids. Electron microscopy shows no evidence that coupling factor represent knobs attached to the surface of the thylakoids.