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

Conditions essential for the preparation of active ammonia-oxidizing extracts of Nitrosomonas europaea were studied. The extracts were unstable during storage and required specific assay conditions for ammonia oxidation. Bovine serum albumin, spermine, or MgCl2 was required for ammonia 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 spermine or MgCl2 at lower phosphate concentrations. Kinetic experiments showed a partial reduction of cytochrome c preceding the initiation of oxygen consumption due to ammonia oxidation.