The electron paramagnetic resonance of molybdenum in rat liver and in rat liver mitochondria

Abstract

1. 1. A spectral feature of the EPR spectrum of rat liver and rat liver mitochondria observed near g = 1.96 arises from a paramagnetic form of molybdenum. Liver mitochondria prepared from untreated control animals, from animals treated with 92Mo ( I = o) or from animals treated with the naturally occurring mixture of molybdenum isotopes show a doublet in the g = 1.96 region while liver mitochondria from rats treated with 95Mo ( I = 5 2 ) show no such EPR absorptions. 2. 2. Resuspension of mitochondria from control animals in sucrose- 2H 2O solution converts the EPR doublet to a singlet suggesting interaction of paramagnetic molybdenum with protons. 3. 3. The addition of NADH to rat liver mitochondria which had been frozen diminishes the resonance ascribable to molybdenum. 4. 4. It is believed that the EPR of molybdenum in rat liver mitochondria, which cannot be observed under the same conditions in beef heart mitochondria, arises from molybdoproteins previously isolated from liver and not from proteins involved in mitochondrial electron transport.