Transition metal and organic radical components of carp liver tissue observed by electron paramagnetic resonance spectroscopy

Paramagnetic transition metal centers and organic radicals in liver from wild-type carp (Cyprinus carpio) were characterized by electron paramagnetic resonance (EPR) spectroscopy. Approximately twelve EPR signals were observed at 77 K with resonance positions between g=1.8 and g=2.5. Identification was facilitated by a study of the variation in signal intensity with microwave power (microwave power saturation) for each signal. Many were organic radical or iron signals from typical liver enzymes, including cytochrome P450, coenzyme Q₁₀, NADH dehydrogenase, and succinate dehydrogenase, cytochrome c oxidase and/or catalase. Of special interest were two signals that are not normally found in mammalian liver. The first was a six-line signal from divalent manganese, which was evident in the spectra in quantities suggestive of a functional role. The second was probably a signal from nitrosylated non-heme iron and may be related to the presence of nitrogen-containing compounds produced by nitrifying bacteria in the aquatic environment. These notable differences between the EPR spectra of fish and mammalian liver suggest major metabolic differences between the two systems.