Spectral and potentiometric analysis of cytochromes from Bacillus subtilis

Bacillus subtilis cytoplasmic membranes contain several cytochromes which are linked to the respiratory chain. At least six different cytochromes have been separated and identified by ammonium sulphate fractionation and ion-exchange chromatography. They include two terminal oxidases with CO-binding properties and cyanide sensitivity. One of these is an aa3-type cytochrome c oxidase which has characteristic absorption maxima in the reduced-oxidized difference spectrum at 601 nm in the alpha-band and at 443 nm in the Soret band regions. In the alpha-band two separate electron transitions with Em = +205 mV and Em = +335 mV can be discriminated by redox potentiometric titration. The other CO-binding cytochrome c oxidase contains two cytochrome b components with alpha-band maxima at 556 nm and 559 nm. Cytochrome b556 can be reduced by ascorbate and has an Em + +215 mV, whereas cytochrome b559 has an Em = +140 mV. Furthermore a complex consisting of a cytochrome b564 (Em = +140 mV) associated with a cytochrome c554 (Em = +250 mV) was found. This cytochrome c554, which can be reduced by ascorbate, appears to have an asymmetrical alpha-peak and stains for heme-catalyzed peroxidase activity on SDS-containing polyacrylamide gels. A protein with a molecular mass of about 30 kDa is responsible for this activity. A cytochrome b559 (Em = +65 mV) appears to be an essential part of succinate dehydrogenase. Finally a cytochrome c550 component with an apparent mid-point potential of Em = +195 mV has been detected.