ATP hydrolysis catalyzed by a beta subunit preparation purified from the chloroplast energy transducing complex...

Washing thylakoid membranes with 1 M LiCl causes the release of the beta subunit from the chloroplast energy transducing complex (CF1.CF0) in spinach chloroplasts. This protein purifies by size exclusion chromatography as a 180-kDa aggregate and, thus, is probably composed of a trimer of beta polypeptides. The purified aggregate binds ADP to a high and a low affinity site with dissociation constants of 15 and 202 microM, respectively. Mg2+ is required for ADP to bind to both sites. Manganese binds to the protein in a cooperative manner to at least two sites with high affinity. The beta subunit preparation catalyzes Mg2+-dependent ATP hydrolysis at rates which are comparable to other subunit-deficient CF1 preparations and is increased by treatments known to activate the Mg2+-ATPase activity of CF1. However, Ca2+ is not an effective cofactor for this reaction and treatments which activate the Ca2+-ATPase of CF1 are either ineffective or inhibitory.