INFLUENCE OF NH_4^+ ON THE OXYGEN UPTAKE OF MITOCHONDRIA ISOLATED FROM CORN AND PEA SHOOTS

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Mitochondria isolated by Percoll density gradient centrifugation from both corn and pea shoots contain approximately 4 nmol NH_4^+ per mg of mitochondrial protein. Higher concentrations of NH_4^+, up to 45 mM, had no effect on the rate of mitochondrial oxygen uptake when malate was used as the respiratory substrate. Oxidation of succinate, citrate, or glycine by either types of mitochondria was also resistant to 20 mM of NH_4^+. The rate of α-ketoglutarate oxidation at state 3 was reduced a little. Thus, oxidative phosphorylation of corn and pea mitochondria was found to be resistant to relatively high concentrations of NH_4^+. Corn mitochondria were also able to oxidize glutamate and its oxidation at state 3 was stimulated slightly by NH_4^+. On the other hand, NH_4^+ reduced the glutamate oxidation by pea mitochondria. Aminooxyacetate (1 mM) strongly inhibited the glutamate oxidation by mitochondria. This result indicates that the major route of glutamate oxidation proceeds via a transamination reaction rather than a direct deamination by glutamate dehydrogenase.
社団法人日本土壌肥料学会の論文