Dissimilatory nitrate metabolism by eukaryotic microorganisms and cytochrome P-450.

1.我发现真菌欧氏镰刀菌可以厌氧还原硝酸盐或亚硝酸盐生成一氧化二氮(N_2O)。这是首次发现真菌显示出强大的反硝化活性，这将是微生物学的一个重要结果。我分离并鉴定了与异化亚硝酸盐还原有关的两种成分。一种细胞色素c(c-553)具有亚硝酸盐还原酶活性，一种已分离的细胞色素P-450(P-450)被证明是一种一氧化氮还原酶。因此，真菌的反硝化系统在一定程度上是分子水平的。P-450的功能是非常独特的，因为P-450是一组具有单加氧酶活性的血红蛋白。因此，P-450超家族成员之间的结构、功能和进化关系提出了非常耐人寻味的问题。除尖孢镰刀菌外，许多真菌都具有反硝化活性。在这些真菌的反硝化过程中，主要产物是N_2O，与Forum的情况一样。几种真菌不能还原硝酸盐。少数真菌，如茄病镰刀菌和圆筒形藻，可由亚硝酸盐生成N_2和N_2O。结果表明，产物N_2中只有一个氮原子来自亚硝酸盐，而N_2O中的两个氮原子都来自亚硝酸盐。从而证明了硝酸盐和亚硝酸盐以外的化合物中的氮原子被用作产物N中的氮原子的对应物。在尖孢镰刀菌中也观察到了这种现象。叠氮或水杨基？草原酸中的氮原子被引入到N2O中作为对应的氮原子，尽管这些化合物不能诱导反硝化活性。这样的“共硝化”是真菌反硝化的独特之处。

1. I found that the fungus Fusarium orum could reduce nitrate or nitrite anaerobically to form nitrous oxide (N_2O). This is the first finding that a fungus exhibits a potent denitrifying activity, and would be an important result in microbiology.2. I isolated and identified two components involved in the dissimilatory nitrite reduction. A cytochrome c(c-553)was shown to exhibit nitrite reductase activity, and a cytochrome P-450(P-450)that had already been isolated (P-450_<dNIR>) was shown to be a nitric oxide reductase. The fungal denitrification system was thus clarit'llien in part at molecular level. The function of P-450_<dNIR> is quite unique, since P-450 has been known as a group of hemeproteins that exhibit monooxygenase activities. P-450_<dNIR> has thus proposed highly intriguing problems with respect to structure, function, and evolutional relationships between members of P-450 superfamily.3. Many fungi other than F. oxysporum were shown to exhibit denitrifying activities. The main product was N_2O in these fungal denitrification as in the case of Forum. Several fungi could not reduce nitrate. A few fungi, such as Fusarium solani and Cylindrocarpon tonkinense, formed N_2 as well as N_2O from nitrite. It was shown that only one nitrogen atom in the product N_2 was derived from nitrite, whereas both nitrogen atoms in N_2O were derived from nitrite. It was thus demonstrated that nitrogen atoms in compounds other than nitrate or nitrite were utilized as a counterpart of nitrogen atoms in the product N. . Such a phenomenon was also observed with F. oxysporum. Nitrogen atoms in azide or salicylhyd?oxamic acid was incorporated into N_2O as a counterpart, although these compounds were not capable of inducing denitrifying activity. Such "co-denitrification" is a unique feature of fungal denitrification.