title: Iron-sulphur centres in mitochondria from Arum maculatum spadix with very high rates of cyanide-resistant respiration.
abstract: X-band electron-paramagnetic-resonance spectroscopy at 4.2--77K combined with measurements of oxidation-reduction potential was used to identify iron--sulphur centres in Arum maculatum (cuckoo-pint) mitochondria. In the oxidized state a signal with a derivative maximum at g = 2.02 was assigned to succinate dehydrogenase centre S-3. Unreduced particles showed additional signals at g = 2.04 and 1.98 (at 9.2 GHz), which may be due to a spin-spin interaction. In the reduced state a prominent signal at g = 1.93 and 2.02 was resolved into at least three components that could be assigned to centres S-1 and S-2 of succinate dehydrogenase (midpoint potentials -7 and -240 mV respectively at pH 7.2) and a small amount of centre N-1b (e'o= -240 mV) of NADH-ubiquinone reductase. In addition, changes in line shape around -10 mV indicated the presence of a fourth component in this signal. The latter was more readily reduced by NADH than by succinate, suggesting that it might be associated with the external NADH dehydrogenase. The iron-sulphur centres of NADH-ubiquinone reductase were present in an unusually low concentration, indicating that the alternative, non-phosphorylating, NADH dehydrogenase containing a low number of iron-sulphur centres may be responsible for most of the high rate of oxidation of NADH.
mesh_terms: D003486:Cyanides; D007506:Iron-Sulfur Proteins / Q000032:analysis*; D008667:Metalloproteins / Q000032:analysis*; D008928:Mitochondria / Q000032:analysis*; D010084:Oxidation-Reduction; D010947:Plants, Toxic / Q000032:analysis*; D013057:Spectrum Analysis
chemical_list: D003486:Cyanides; D007506:Iron-Sulfur Proteins; D008667:Metalloproteins