Abstract

Mass spectrometric determinations of O2 affinities by the rumen fungus Neocallimastix patriciarum indicated a stable respiration under liquid phase O2 concentrations up to 10 μM, the apparent Km for O2 under these conditions was 4.0 μM. Exposure to O2 concentrations in excess of 10 μM resulted in rapid inactivation of the observed respiration. Calculated H2 evolution rates for the organism are 8.1 nmol min-1 per mg of protein. Exposure to liquid-phase O2 concentrations in excess of 1.4 μM caused 50% inhibition of H2 production. That superoxide and peroxide are amongst the products of respiration was shown by the use of ESR spectroscopy with the spin trapping agent 5,5-dimethyl-l-pyrroline-N-oxide. An active superoxide dismutase was present, but catalase could not be detected.

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