Department of Agricultural Chemistry, Faculty of Agriculture, Kobe University, Rokkodai-cho, Nada-ku, Kobe 657, Japan.
Plant Physiol. 1987 Mar;83(3):472-4. doi: 10.1104/pp.83.3.472.
Inorganic orthophosphate (25 millimolar in assay media; Pi) was found to increase in vitro activity of NADH-nitrate reductase (NR) isolated from 2-row barley (Hordeum vulgare L.) leaves with a saturating concentration of nitrate (2 millimolar) but to decrease it with low nitrate levels (<0.1 millimolar). The response to nitrate concentrations was Pi specific. The Lineweaver-Burk plot showed that Pi increases the apparent K(m) for nitrate as well as V(max), whereas it does not alter the K(m) for NADH significantly. These results suggest that the interaction between a molybdenum site of the enzyme and Pi results in alteration of the properties of NR molecule.
无机正磷酸盐（测定介质中 25 毫摩尔；Pi）被发现可增加离体条件下从 2 棱大麦（Hordeum vulgare L.）叶片中分离得到的 NADH-硝酸还原酶（NR）的活性，此时硝酸的浓度为 2 毫摩尔，而当硝酸盐水平较低（<0.1 毫摩尔）时，其活性则降低。对硝酸盐浓度的响应是 Pi 特异性的。Lineweaver-Burk 作图表明，Pi 增加了硝酸盐的表观 K(m)和 V(max)，而对 NADH 的 K(m)影响不大。这些结果表明，酶的钼位点与 Pi 之间的相互作用导致 NR 分子性质的改变。
