Abstract
Nitrobacter agilis, which contains a very active nitrite dehydrogenase, was studied in vivo under anaerobic conditions by the “NNMR technique. When incubated with equimolar 16N0; and unlabeled nitrite (or 15NO; and unlabeled nitrate) the bacterium catalyzed an isotope exchange reaction at rates about 10% those observed in the nitrite oxidase assay. When incubated with leO-labeled “NO, and 180-labeled “NO;, the ”0 was observed to exchange at similar rates from both species into water. Finally, when incubated with equimolar [“Olnitrate and “NO;, intermolecular “0 transfer was observed to result in formation of double labeled nitrate and nitrite at similar rates. “0 was transferred from nitrate to a 16N species or to water at approximately equal rates under the conditions of the experiments. It is argued that the enzyme responsible for these exchange reactions is nitrite dehydrogenase and not nitrate reductase. This work and the related experiments of DiSpirito and Hooper (DiSpirito, A. A., and Hooper, A. B. (1986) J.Biol. Chem. 261, 10534- 10537)represent the first demonstrations of intermolecular oxygen atom transfer among oxotransferases. Mechanistic implications are discussed.