Exploration of respiratory chain of Nocardia asteroides: purification of succinate quinone oxidoreductase

Nocardia asteroides is a pathogenic bacterium that causes severe pulmonary infections and plays a vital role in HIV development. Its electron transport chain containing cytochromes as electron carriers is still undiscovered. Information regarding cytochromes is important during drug synthesis based on cytochrome inhibitions. In this study we explored the electron transport of N. asteroides. Spectroscopic analysis of cytoplasm and membranes isolated from N. asteroides indicates the presence of soluble cytochrome-c, complex-II and the modified a(1)c(1) complex as the terminal oxidase. The molecular weight of the respiratory complex-II isolated and purified from the given bacterium was 103 kDa and was composed of three subunits, of 14, 26 and 63 kDa. Complex-II showed symmetrical α-absorption peaks at 561 nm in the reduced state. Spectral analysis revealed the presence of only one heme b molecule (14-kDa subunit) in complex-II, which was confirmed by heme staining. Heme b content was found to be 9.5 nmol/mg in complex-II. The electron transport chain of N. asteroides showed the presence of soluble cytochrome-c, cytochrome-a(1)c(1) and cytochrome-b