Purification of a manganese-containing protein involved in photosynthetic oxygen evolution and its use in...

Extraction of thylakoid membranes with cholate in the presence of ammonium sulfate inactivated oxygen evolution and liberated a managanese-containing protein. This protein could be combined with preformed liposomes containing the depleted thylakoid membranes to restore 85% of the original oxygen-evolution activity. The protein did not affect the primary photochemical events of photosystem I or photosystem II, and it was required only for electron transport in which water was the electron donor. The protein has been purified to homogeneity and has an apparent molecular weight of 65,000 (polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate). Atomic absorption revealed two atoms of manganese bound to each 65,000-dalton protein molecule. Treatment with alkaline Tris removed the bound manganese and rendered the protein incapable of restoring oxygen evolution; however, Tris treatment of the depleted membranes before reconstitution had no effect. Thus, this manganese protein is probably the site of Tris action in isolated chloroplasts and is at least part of the water-oxidation enzyme system.