Schrader L E, Hageman R H
Department of Agronomy, University of Illinois, Urbana, Illinois 61801.
Plant Physiol. 1967 Dec;42(12):1750-6. doi: 10.1104/pp.42.12.1750.
Primary and secondary metabolites of inorganic nitrogen metabolism were evaluated as inhibitors of nitrate reductase (EC 1.6.6.1) induction in green leaf tissue of corn seedlings. Nitrite, nitropropionic acid, ammonium ions, and amino acids were not effective as inhibitors of nitrate reductase activity or synthesis. Increasing alpha-amino nitrogen and protein content of intact corn seedlings by culture techniques significantly enhanced rather than decreased the potential for induction of nitrate reductase activity in excised seedlings.Secondary metabolites, derived from phenylalanine and tyrosine, were tested as inhibitors of induction of nitrate reductase. Of the 9 different phenylpropanoid compounds tested, only coumarin, trans-cinnamic and trans-o-hydroxycinnamic acids inhibited induction of nitrate reductase.While coumarin alone exhibited a relatively greater inhibitory effect on enzyme induction than on general protein synthesis (the latter measured by incorporation of labeled amino acids), this differential effect may have been dependent upon unequal rates of synthesis and accumulation with respect to the initial levels of nitrate reductase and general proteins. Because of the short half-life of nitrate reductase, inhibitors of protein synthesis in general could still achieve differential regulation of nitrogen metabolism. Coumarin did not inhibit nitrate reductase activity when added directly to the assay mixture at 5 mm.Carbamyl phosphate and its chemical derivative, cyanate, were found to be competitive (with nitrate) inhibitors of nitrate reductase. The data suggest that cyanate is the active inhibitor in the carbamyl phosphate preparations.
无机氮代谢的初级和次级代谢产物被评估为玉米幼苗绿叶组织中硝酸还原酶（EC 1.6.6.1）诱导的抑制剂。亚硝酸盐、硝基丙酸、铵离子和氨基酸作为硝酸还原酶活性或合成的抑制剂无效。通过培养技术提高完整玉米幼苗的α-氨基氮和蛋白质含量，显著增强而非降低了离体幼苗中硝酸还原酶活性的诱导潜力。源自苯丙氨酸和酪氨酸的次级代谢产物被测试为硝酸还原酶诱导的抑制剂。在所测试的9种不同的苯丙烷类化合物中，只有香豆素、反式肉桂酸和反式邻羟基肉桂酸抑制硝酸还原酶的诱导。虽然单独的香豆素对酶诱导的抑制作用比对一般蛋白质合成的抑制作用相对更大（后者通过标记氨基酸的掺入来测量），但这种差异效应可能取决于相对于硝酸还原酶和一般蛋白质的初始水平，合成和积累的速率不相等。由于硝酸还原酶的半衰期较短，一般的蛋白质合成抑制剂仍然可以实现对氮代谢的差异调节。当以5 mM直接添加到测定混合物中时，香豆素不抑制硝酸还原酶活性。发现氨基甲酰磷酸及其化学衍生物氰酸盐是硝酸还原酶的竞争性（与硝酸盐）抑制剂。数据表明，氰酸盐是氨基甲酰磷酸制剂中的活性抑制剂。
