Quinol - cytochrome c Oxidoreductase from the Thermophilic Bacterium PS 3 PURIFICATION AND PROPERTIES OF A CYTOCHROME bcl

A quinol-cytochrome c oxidoreductase (cytochrome b c l complex) has been purified from plasma membranes of a thermophilic Bacillus, PS3, by ion-exchange chromatography in the presence of Triton X100. The purified enzyme shows absorption bands at 561-562 nm and 553 nm at room temperature, and 560, 551, and 547 nm at 80 K upon reduction, and gives an ESR signal similar to that of a Rieske-type iron sulfur center. Its contents of protohemes, heme c, and non-heme iron are about 23, 10, and 21 nmol/mg of protein, respectively. The enzyme consists of four polypeptides with molecular masses of 29, 23, 21, and 14 kDa judging from their electrophoretic mobilities in the presence of sodium lauryl sulfate. Since the staining intensities of the respective bands are almost proportional to their molecular masses, the monomer complex (87 kDa) of the subunits probably consists of a cytochrome b having two protohemes, a cytochrome c1 and an Fe2-Sz-type iron sulfur center. The 29 and 2 1 kDa subunits were identified as cytochromes c1 and b, respectively, and the 23-kDa subunit is probably an iron-sulfur protein, since the 14-kDa polypeptide can be removed with 3 M urea without reducing the content of non-heme iron. Several characteristics of the subunits and chromophores indicate that the PS3 enzyme is rather similar to cytochrome bef (a b c l complex equivalent) of chloroplasts and Cyanobucteria. The PS3 complex catalyzes reduction of cytochrome c with various quinol compounds in the presence of Plipids and menaquinone. The turnover number at pH 6.8 was about 5 8-l at 40 “C and 50 8-l at 60 “C. The enzyme is heat-stable up to 65 “C.