High Yield Purification of a Four Subunit caa3-Type Cytochrome Oxidase from the Thermophilic Bacterium Bacillus PS3 Using Fast Protein Liquid Chromatography

Abstract

The thermophilic bacterium, Bacillus PS3, was grown in a vigorously aerated nutrient broth at 65°C with 100 mM glutamic acid serving as a supplemental carbon and nitrogen source, These growth conditions resulted in membranes highly enriched in cytochrome c oxidase (COX) [23.32 ± 4.32 nmol heme a/g of cells (n = 5)], which is nearly a threefold higher concentration of COX (heme caa3-type) than previously reported for this organism, A new high-yield purification of COX was performed by extracting the bacterial membranes with Triton X-100 (7 mg/mg protein), followed by ion-exchange fast liquid protein chromatography using a QAE (trimethyl ammonium) resin with subsequent hydroxyapatite chromatography and ammonium sulfate fractionation. This purification regime resulted in a 16% yield of cytochrome c oxidase with 20 mg of pure caa3-type COX (13 nmol heme a/mg protein) isolated from 100 g of cells, SDS-PAGE showed that the isolated enzyme had four subunits with apparent Mr of 68, 38, 23, and 13 kDa, In addition, a new 34-kDa peptide was also detected in this preparation, which may represent the ORF1 gene product for this organism, Subunit II (Mr = 38 M) of the isolated enzyme was shown to contain covalently bound heme c by using both heme-staining of SDS-PAGE and immunoreactivity with an anti-cytochrome c antibody. The purified enzyme also exhibited high electron transfer activity (340 s−1) when assayed at pH 6.5 in the presence of the nonionic detergent, β-dodecyl maltoside.