Department of Genetics and Cell Biology, University of Minnesota, St. Paul, Minnesota 55108.
Proc Natl Acad Sci U S A. 1982 Oct;79(19):5871-5. doi: 10.1073/pnas.79.19.5871.
The (18)O/(16)O shifts in (15)N NMR were determined for nitrite (0.13 ppm or 4.2 Hz at 7.05 T) and nitrate (0.056 ppm or 1.7 Hz at 7.05 T) at neutral pH. The technique, which allows clear differentiation between (16)O and (18)O derivatives of (15)N, was used to assess the source of oxygens in nitrite produced by oxidation of ammonia in Nitrosomonas. The two oxygens of nitrite produced by cell-catalyzed oxidation of ammonia or hydroxylamine had the (16)O/(18)O isotope composition of water. Nitrosomonas is shown to catalyze the rapid exchange of oxygen between nitrite and water. The exchange reaction required the concomitant oxidation of ammonia. The amount of nitrite exchanged could exceed the amount of ammonia oxidized by a factor of 3. This exchange explains previous difficulties in the determination of the source of nitrite oxygen in ammonia oxidation. When cells oxidized [(15)N]ammonia in the presence of a great excess of exogenous [(14)N]nitrite, 20% of one oxygen in the resulting [(15)N]nitrite was derived from dioxygen. Dioxygen is apparently the source of at least one oxygen in nitrite produced by Nitrosomonas.
中性 pH 条件下，通过测定亚硝酸根（7.05T 时 0.13ppm 或 4.2Hz）和硝酸根（7.05T 时 0.056ppm 或 1.7Hz）的 (18)O/(16)O 位移，确定了氨氧化菌（Nitrosomonas）中，由氨氧化生成的亚硝酸根中氧原子的来源。该技术可清晰区分 (15)N 的 (16)O 和 (18)O 衍生物，用于评估亚硝酸根中氧原子的来源。细胞催化氨或羟胺氧化生成的亚硝酸根的两个氧原子具有水的 (16)O/(18)O 同位素组成。实验表明，亚硝酸根可与水之间发生快速氧交换反应，且该交换反应需要同时发生氨氧化。交换反应生成的亚硝酸根量可超过氨氧化量的 3 倍。这一交换反应解释了之前在确定氨氧化过程中，亚硝酸根氧原子来源时所遇到的困难。当细胞在大量外源 (14)N 亚硝酸根存在的条件下氧化 [(15)N]氨时，生成的 [(15)N]亚硝酸根中，有 20%的氧来源于分子氧。显然，分子氧是亚硝酸根生成的氧原子来源之一。
