Paramagnetic Resonance Absorption of cytochrome c in the frequency Range 20-50 MHz.

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It was reported by the authers that the electronic state of <Fe^(3+)> of the oxidized cytochrome <c_3> is a low spin state and the heme-heme spin interaction was observed to be more than about ten times than expected. The interaction consists of two components; the dipolar interaction, <W_(> alpha <:p)> and the exchange interaction, Wex. The results obtained by us suggested that Wex>> <W_(> alpha <:p)> . In ordef to investigate the interaction directly, the frequency dependence of the absorption shape in the paramagnetic resonance has been measured in the microwave frequency range between 20 and 50 MHz, where <mu> Hres may grow up into the interaction energy as the frequency is increased. We have tried to observe the resonance absorption at temperatures down to 1.4 K, but we have not clearly observe any absorption. Considering the sensitivity of our ESR apparatus, the absorption line width may be estimated as several tens Oersteds which may come from the dipolar interaction. Therefore, on the contrary of our expectation, we may conclude that Wex<< <W_(> alpha <:p)> .