Garrett R H, Cove D J
Mol Gen Genet. 1976 Dec 8;149(2):179-86. doi: 10.1007/BF00332887.
Mutants of A. nidulans at several loci lack detectable NADPH-nitrate reductase activity. These loci include niaD, the structural gene for the nitrate reductase polypeptide, and five other loci termed cnxABC, E, F, G and H which are presumed to be involved in the formation of a molybdenum-containing component (MCC) necessary for nitrate reductase activity. When forzen mycelia from A. nidulans deletion mutant niaD26 were homogenized in a Ten Broeck homogenizer together with frozen mycelia from either cnxA6, cnxE29, cnsF12, cnxG4 or cnxH3 strains grown on urea + nitrate as the nitrogen source, nitrate reductase activity was detectable in the extract. Similar results were obtained by co-homogenizind niaD mycelia with Neurospora crassa nit-1 mycelia induced on nitrate. Thus, all A. nidulans cnx mutants are similar to the N. crassa nit-1 strain in their capacity to yield NADPH-nitrate reductase in the presence of the presumed MCC. As judged by the amounts of nitrate reductase formed, niaD26 mycelia grown on urea +/- nitrate contained much more available MCC than ammonium-grown mycelia. No NADPH-nitrate reductase activity was found in extracts prepared by co-homogenizing mycelia from all five A. nidulans cnx strains. Wild-type A. nidulans NADPH-nitrate reductase acid dissociated by adjustment to pH 2.0-2.5 AND RE-ADJUSTED TO PH 7 could itself re-assemble to form active nitrate reductase and thus was not a useful source of MCC for these experiments. These results are consistent with the conclusion that the active nitrate reductase complex is composed of polypeptide components which are the niaD gene product, plus the MCC which is formed through the combined action of the cnx gene products. Further, the production of MCC may be regulated in response to the nitrogen nutrition available to the organism.
构巢曲霉多个基因座的突变体缺乏可检测到的NADPH - 硝酸还原酶活性。这些基因座包括niaD，即硝酸还原酶多肽的结构基因，以及其他五个基因座，分别称为cnxABC、E、F、G和H，据推测它们参与了硝酸还原酶活性所必需的含钼组分（MCC）的形成。当将构巢曲霉缺失突变体niaD26的冷冻菌丝体与以尿素 + 硝酸盐作为氮源生长的cnxA6、cnxE29、cnsF12、cnxG4或cnxH3菌株的冷冻菌丝体一起在Ten Broeck匀浆器中匀浆时，提取物中可检测到硝酸还原酶活性。通过将niaD菌丝体与在硝酸盐上诱导的粗糙脉孢菌nit - 1菌丝体共同匀浆也获得了类似结果。因此，所有构巢曲霉cnx突变体在存在假定的MCC时产生NADPH - 硝酸还原酶的能力与粗糙脉孢菌nit - 1菌株相似。根据形成的硝酸还原酶的量判断，在尿素±硝酸盐上生长的niaD26菌丝体比在铵上生长的菌丝体含有更多可用的MCC。通过将所有五个构巢曲霉cnx菌株的菌丝体共同匀浆制备的提取物中未发现NADPH - 硝酸还原酶活性。野生型构巢曲霉NADPH - 硝酸还原酶通过调节至pH 2.0 - 2.5进行酸解离，再调节至pH 7后自身可重新组装形成活性硝酸还原酶，因此不是这些实验中MCC的有用来源。这些结果与以下结论一致：活性硝酸还原酶复合物由niaD基因产物的多肽组分以及通过cnx基因产物的联合作用形成的MCC组成。此外，MCC的产生可能会根据生物体可利用的氮营养进行调节。
