Wallace W
Biochim Biophys Acta. 1975 Feb 19;377(2):239-50. doi: 10.1016/0005-2744(75)90306-x.
Evidence is presented which suggests that the NAD(P)H-cytochrome c reductase component of nitrate reductase is the main site of action of the inactivating enzyme. When tested on the nitrate reductase (NADH) from the maize root and scutella, the NADH-cytochrome c reductase was inactivated at a greater rate than was the FADH2-nitrate reductase component. With the Neurospora nitrate reductase (NADPH) only the NADPH-cytochrome c reductase was inactivated. p-Chloromercuribenzoate at 50 muM, which gave almost complete inhibition of the NADH-cytochrome c reductase fraction of the maize nitrate reductase, had no marked effect on the action of the inactivating enzyme. A reversible inactivation of the maize nitrate reductase has been shown to occur during incubation with NAD(P)H. In contrast to the action of the inactivating enzyme, it is the FADH2-nitrate reductase alone which is inactivated. No inactivation of the Neurospora nitrate reductase was produced by NAD(P)H alone and also in the presence of FAD. The lack of effect of the inactivating enzyme and NAD(P)H on the FADH2-nitrate reductase of Neurospora suggests some differences in its structure or conformation from that of the maize enzyme. A low level of cyanide (0.4 mu M) markedly enhanced the action of NAD(P)H on the maize enzyme; Cyanide at a higher level (6 mu M) did give inactivation of the Neurospora nitrate reductase in the presence of NADPH and FAD. The maize nitrate reductase, when partially inactivated by NADH and cyanide, was not altered as a substrate for the inactivating enzyme. The maize root inactivating enzyme was also shown to inactivate the nitrate reductase (NADH) in the pea leaf. It had no effect on the nitrate reductase from either Pseudomonas denitrificans or Nitrobacter agilis.
有证据表明，硝酸还原酶的NAD(P)H - 细胞色素c还原酶成分是失活酶的主要作用位点。在用玉米根和盾片中的硝酸还原酶（NADH）进行测试时，NADH - 细胞色素c还原酶的失活速率比FADH2 - 硝酸还原酶成分更快。对于粗糙脉孢菌硝酸还原酶（NADPH），只有NADPH - 细胞色素c还原酶被失活。50μM的对氯汞苯甲酸几乎完全抑制了玉米硝酸还原酶的NADH - 细胞色素c还原酶部分，但对失活酶的作用没有显著影响。已证明玉米硝酸还原酶在与NAD(P)H孵育期间会发生可逆失活。与失活酶的作用相反，只有FADH2 - 硝酸还原酶被失活。单独的NAD(P)H以及在有FAD存在的情况下，都不会使粗糙脉孢菌硝酸还原酶失活。失活酶和NAD(P)H对粗糙脉孢菌的FADH2 - 硝酸还原酶缺乏作用，这表明其结构或构象与玉米酶存在一些差异。低水平的氰化物（0.4μM）显著增强了NAD(P)H对玉米酶的作用；较高水平的氰化物（6μM）在有NADPH和FAD存在的情况下确实会使粗糙脉孢菌硝酸还原酶失活。当玉米硝酸还原酶被NADH和氰化物部分失活时，作为失活酶的底物并没有改变。玉米根中的失活酶也被证明能使豌豆叶中的硝酸还原酶（NADH）失活。它对反硝化假单胞菌或活跃硝化杆菌的硝酸还原酶没有影响。
