Assimilatory nitrate reductase of some soil bacteria.

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Abstract
To elucidate the nature of bacterial assimilatory nitrate reductase, one attempted to use bacteria which contain assimilatory but not dissimilatory nitrate reductase. Four strains of bacteria (M-1, M-2, M-3 and J-1), isolated in this study, and Nocardia globerula IFO 13509 had such characteristics; they grew in a medium containing nitrate as the sole N source and did not accumulate nitrite, ammonia or N2 during growth in nitrate synthetic complex media with or without aeration. Strains M-1, M-2, and M-3 are Bacillus spp., which are identical to or closely resemble B. megaterium, and strain J-1 is a Pseudomonas sp. which resembles P. hydrogenovora. Resting cells of these bacteria assimilated nitrate in the presence of glucose or pyruvate without accumulation of nitrite. Assimilatory nitrate reductase in cell-free extracts from the bacteria reduced nitrate if NADPH or NADH was added as an electron donor. NADPH and NADH served as the donor for the enzymes from M-1 and M-2, while only NADPH was the effective donor for the enzymes from M-3, J-1 and N. globerula. All the enzymes from these bacteria were predominantly localized in the soluble cytoplasmic fraction. Effects of inhibitors, such as KCIO3, NaN3, NH2OH and p-chloromercuribenzoate, were variable when one of the inhibitors was tested for the enzymes from different strains, but inhibition was similar when tested on the enzyme from the same strain (M-1 or M-2) with NADPH or NADH. The enzymes from M-1, M-3 and J-1 were inhibited by 1 mM KCIO3, but the enzymes from M-2 and N. globerula were not inhibited; the enzyme from M-2 was not inhibited by 1 mM NaN3, but the enzymes from the other strains were inhibited.

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