Electron paramagnetic resonance characterization of membrane bound iron-sulfur clusters and aconitase in plant mitochondria

Electron paramagnetic resonance (EPR) characteristics of the iron-sulfur clusters of potato tuber mitochondria have been examined in various subfractions of the mitochondria. We confirm that EPR signals comparable to those of the iron-sulfur proteins of mammalian mitochondria respiratory complexes are also present in plant mitochondria. Two distinct iron-sulfur centers paramagnetic in the oxidized state exhibit signals which differ in their detailed line shape and field position. One of these which is present in the inner membrane corresponds to center S.3. The EPR spectrum of the soluble fraction revealed the presence of another center with a low field maximum at g = 2.03 and is associated with aconitase. The EPR signal observed in the mitochondrial matrix from potato tuber and characteristic of 3Fe cluster is significantly changed in shape after addition of citrate and differs clearly from the spectrum of pig heart mitochondrial aconitase. The aconitase in plant mitochondria differs from that of mammalian mitochondria by several features.