Studies on Denitrification: XIV.*The Electron Donating System in the Reduction of Nitric Oxide and Nitrate

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Abstract
The electron donating mechanism of the reduction of NO to N2O by the particles of Pseudomonas denitrificans was studies, using phenazine methosulfate reduced with ascorbate (ascorbate-PMS-NO system) and lactate (lactate-NO system) as the electron donor, and the following facts were found. 1. A lag in the NO uptake was observed on the reaction with the lactate-NO system but not with the ascorbate-PMS-NO system. The specific activity of the latter system was about three times as high as that of the former. 2. Spectrophotometry under the atmosphere of 10% NO plus 90% argon suggested that b-type cytochrome(s) and particulate cytochrome c-552 participate in the reduction of NO to N2O with both systems. 3. BAL, HOQNO or antimycin A inhibited the nitric oxide reduction in both systems. 4. Addition of nitrate to the lactate-NO system remarkably suppressed the nitric oxide reduction, and nitrate was reduced to nitrite. The ratio of the rate of nitrate reduction to that of nitric oxide reduction was larger than 1. Based on the observations that nitrate reduction resulted in oxidation of a b-type cytochrome and was not inhibited by BAL, antimycin A or HOQNO, the site of interaction of nitrate was concluded to be the b-type cytochrome. A possible electron transport mechanism in the cellular particles of Ps. denitrificans was discussed from these results.

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