The cytochrome complement of Haemophilus parasuis

Abstract

Spectral analyses with subcellular fractions derived from Haemophilus parasuis demonstrated that this organism could synthesize membrane-bound and soluble CO- and NO-binding c-type cytochromes in addition to the membrane-bound cytochromes d, a1, b, and c; cytochromes d, a1, and o were identified as potential oxidases. The membrane-bound and soluble CO- and NO-binding cytochromes c were not spectrally variant cytochromes c, and the redox properties of the soluble cytochrome (reducible by NADH but not by succinate or ascorbate plus N,N,N′,N′-tetramethyl-p-phenylenediamine) suggested that it, at least, was a low-potential cytochrome; up to 68% of the soluble cytochrome c could be released from the organisms by osmotic-shock treatment, demonstrating its extracytoplasmic location. The cytochrome content of H. parasuis was influenced by both the composition of the growth medium and the phase of growth; it is suggested that the bacterial concentration and growth rate, and therefore the availability of oxygen, regulated cytochrome synthesis.