Assignment of EPR transitions in a manganese-containing lipoxygenase and prediction of local structure
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A new variant of lipoxygenases, one containing manganese instead of iron, is characterized by electron paramagnetic resonance (EPR) at two frequencies. In the manganous state (Se = 5/2), maganese lipoxygenase (MnLO) yields very broad X-band (9.2 GHz) EPR signals, extending over about 800 mT. In contrast, at W-band (94 GHz), the signal is much simplified, consisting of nested transitions centered near the free electrong-value. Computer simulation has been employed to derive estimates of the zero-field splittings for MnLO, with data from these two EPR frequencies. The general features of both X- and W-band spectra are fit, first, by simulations with Se = 5/2, but no nuclear hyperfine splitting. The simulations are then refined by inclusion of the hyperfine splitting. On the basis of the simulations, the ranges of zero-field splitting parameters areD = +0.07 to +0.10 cm−1, andE/D = 0.13 to 0.23. Comparison of the value ofD for MnLO with that of other manga-nese-containing proteins suggests that MnLO has three N-ligands to the metal center and O-ligands in the remainder of 6 coordination positions. The coordination environment of MnLO is similar to that in iron lipoxygenases.
KeywordsElectron Paramagnetic Resonance Electron Paramagnetic Resonance Spectrum Hyperfine Splitting Electron Paramagnetic Resonance Measurement Electron Paramagnetic Resonance Transition
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