Cell-free ammonia-oxidizing system of Nitrosomonas europaea: general conditions and properties

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Abstract
Conditions essential for the preparation of active NH3-oxidizing extracts of N. europaea were studied. The extracts were unstable during storage and required specific assay conditions for NH3 oxidation. Bovine serum albumin, spermine or MgCl2 was required for NH3 oxidation and the concentration of phosphate determined the relative effectiveness of each activator, i.e., albumin being most effective in 0.1 M phosphate and spermin or MgCl2 at lower phosphate concentrations. Kinetic experiments showed a partial reduction of cytochrome c preceding the initiation of O2 consumption due to NH3 oxidation.