Magnetic susceptibility measurements on Pseudomonas cytochrome cd1

The magnetic susceptibilities of cytochrome cd1 from Pseudomonas aeruginosa (American Type Culture Collection 19429) have been measured by a nuclear magnetic resonance technique. In the oxidized form both heme c and heme d1 are in the low-spin state with an average magnetic moment of 2.6 Bohr magnetons. At 25 degrees C and pH 8.0, the ascorbate-reduced cytochrome contains one low-spin and one high-spin heme per subunit. Based on previous reports in the literature, the high-spin ferrous heme has been assigned to the heme d1 group. At pH 8.0 the ascorbate-reduced heme d1 has a magnetic moment of 5.3 Bohr magnetons. This value decreases to 4.9 at pH 5.5, but is still indicative of a high-spin ferrous system. The paramagnetic susceptibility of the ferricytochrome demonstrated a temperature dependence consistent with Curie's law, but the ferrocytochrome showed an increase in paramagnetic susceptibility with increasing temperature.