The metabolism of nitrate and nitrite in the sheep. 2. Hydrogen donators in nitrate reduction by rumen micro-organisms in vitro

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Abstract
Hydrogen is a very active donator for the reduction of nitrate, nitrite and hydroxylamine to ammonia, in the presence of washed micro-organisms from sheep rumen. Nitrite is an intermediary in the reduction of nitrate, and appears transitorily in the early stages of reduction by hydrogen. The pH optima of nitrate and nitrite reduction in an atmosphere of H2 are 6.5 and 5.6, respectively, whereas the opt. for hydroxylamine reduction shows a broad plateau over the range of pH 6-7. Formate, succinate, lactate, citrate, glucose, malate and mannitol are H donators for nitrate reduction, but at lower rates than H. Glycerol, xylose and ethanol have little activity and acetate, propionate and n-butyrate are inactive.