Stouthamer A H
Department of Microbiology, Faculty of Biology, Vrije Universiteit, Amsterdam, The Netherlands.
J Bioenerg Biomembr. 1991 Apr;23(2):163-85. doi: 10.1007/BF00762216.
Under anaerobic circumstances in the presence of nitrate Paracoccus denitrificans is able to denitrify. The properties of the reductases involved in nitrate reductase, nitrite reductase, nitric oxide reductase, and nitrous oxide reductase are described. For that purpose not only the properties of the enzymes of P. denitrificans are considered but also those from Escherichia coli, Pseudomonas aeruginosa, and Pseudomonas stutzeri. Nitrate reductase consists of three subunits: the alpha subunit contains the molybdenum cofactor, the beta subunit contains the iron sulfur clusters, and the gamma subunit is a special cytochrome b. Nitrate is reduced at the cytoplasmic side of the membrane and evidence for the presence of a nitrate-nitrite antiporter is presented. Electron flow is from ubiquinol via the specific cytochrome b to the nitrate reductase. Nitrite reductase (which is identical to cytochrome cd1) and nitrous oxide reductase are periplasmic proteins. Nitric oxide reductase is a membrane-bound enzyme. The bc1 complex is involved in electron flow to these reductases and the whole reaction takes place at the periplasmic side of the membrane. It is now firmly established that NO is an obligatory intermediate between nitrite and nitrous oxide. Nitrous oxide reductase is a multi-copper protein. A large number of genes is involved in the acquisition of molybdenum and copper, the formation of the molybdenum cofactor, and the insertion of the metals. It is estimated that at least 40 genes are involved in the process of denitrification. The control of the expression of these genes in P. denitrificans is totally unknown. As an example of such complex regulatory systems the function of the fnr, narX, and narL gene products in the expression of nitrate reductase in E. coli is described. The control of the effects of oxygen on the reduction of nitrate, nitrite, and nitrous oxide are discussed. Oxygen inhibits reduction of nitrate by prevention of nitrate uptake in the cell. In the case of nitrite and nitrous oxide a competition between reductases and oxidases for a limited supply of electrons from primary dehydrogenases seems to play an important role. Under some circumstances NO formed from nitrite may inhibit oxidases, resulting in a redistribution of electron flow from oxygen to nitrite. P. denitrificans contains three main oxidases: cytochrome aa3, cytochrome o, and cytochrome co. Cytochrome o is proton translocating and receives its electrons from ubiquinol. Some properties of cytochrome co, which receives its electrons from cytochrome c, are reported.(ABSTRACT TRUNCATED AT 400 WORDS)
在存在硝酸盐的厌氧环境下，反硝化副球菌能够进行反硝化作用。文中描述了参与硝酸还原酶、亚硝酸还原酶、一氧化氮还原酶和氧化亚氮还原酶的还原酶的特性。为此，不仅考虑了反硝化副球菌的酶的特性，还考虑了大肠杆菌、铜绿假单胞菌和施氏假单胞菌的酶的特性。硝酸还原酶由三个亚基组成：α亚基含有钼辅因子，β亚基含有铁硫簇，γ亚基是一种特殊的细胞色素b。硝酸盐在膜的细胞质一侧被还原，并提供了存在硝酸盐 - 亚硝酸盐反向转运体的证据。电子流从泛醇经特定的细胞色素b流向硝酸还原酶。亚硝酸还原酶（与细胞色素cd1相同）和氧化亚氮还原酶是周质蛋白。一氧化氮还原酶是一种膜结合酶。bc1复合体参与电子流向这些还原酶的过程，整个反应发生在膜的周质一侧。现在已经确定，NO是亚硝酸盐和氧化亚氮之间的必需中间体。氧化亚氮还原酶是一种多铜蛋白。大量基因参与钼和铜的获取、钼辅因子的形成以及金属的插入。据估计，至少40个基因参与反硝化过程。反硝化副球菌中这些基因表达的调控完全未知。作为这种复杂调控系统的一个例子，描述了大肠杆菌中fnr、narX和narL基因产物在硝酸还原酶表达中的功能。讨论了氧气对硝酸盐、亚硝酸盐和氧化亚氮还原作用影响的调控。氧气通过阻止细胞摄取硝酸盐来抑制硝酸盐的还原。在亚硝酸盐和氧化亚氮的情况下，还原酶和氧化酶之间对来自初级脱氢酶的有限电子供应的竞争似乎起着重要作用。在某些情况下，由亚硝酸盐形成的NO可能抑制氧化酶，导致电子流从氧气重新分配到亚硝酸盐。反硝化副球菌含有三种主要的氧化酶：细胞色素aa3、细胞色素o和细胞色素co。细胞色素o进行质子转运并从泛醇接收电子。报道了从细胞色素c接收电子的细胞色素co的一些特性。（摘要截选至400字）
