Purification of the β Subunit of the Chloroplast H+-Translocating ATPase of Spinach Thylakoids

A significant portion of the catalytic site of CF0-CF1 is located on the β subunit (for a review, see (1)). This enzyme contains three copies of the β subunit which suggests that there are three active sites. Experiments that involve isotope exchange (2), substrate trapping (3) and binding of Mn (4) suggest that at least two of the active sites are coupled. Soluble CF1 is a latent ATPase that can be activated by a variety of procedures (5), some of which are believed to require the exchange of disulfide bonds of the γ subunit (6).