Large-scale purification of active cytochrome b6/f complex from spinach chloroplasts.

A preparation is described through which large quantities of pure, active cytochrome b6/f complex can be isolated from spinach chloroplasts. The resulting complex is at least 90% pure with respect to the maximum content of redox centers, consists of four polypeptides according to polyacrylamide gel electrophoresis, and lacks both ferredoxin: NADP+ oxidoreductase and the high molecular weight form of cytochrome f seen in some other preparations. The complex contains 2 mol b6 and 2 atoms of nonheme iron per mole of cytochrome f, and possesses a high plastoquinol-plastocyanin oxidoreductase activity (Cyt f turnover no. 20-35 s-1). The present preparation should be helpful in the effort to crystallize the cytochrome b6/f complex.