Harms N, van Spanning R J
Department of Microbiology, Vrije Universiteit, Amsterdam, The Netherlands.
J Bioenerg Biomembr. 1991 Apr;23(2):187-210. doi: 10.1007/BF00762217.
Paracoccus denitrificans is able to grow on the C1 compounds methanol and methylamine. These compounds are oxidized to formaldehyde which is subsequently oxidized via formate to carbon dioxide. Biomass is produced by carbon dioxide fixation via the ribulose biphosphate pathway. The first oxidation reaction is catalyzed by the enzymes methanol dehydrogenase and methylamine dehydrogenase, respectively. Both enzymes contain two different subunits in an alpha 2 beta 2 configuration. The genes encoding the subunits of methanol dehydrogenase (moxF and moxI) have been isolated and sequenced. They are located in one operon together with two other genes (moxJ and moxG) in the gene order moxFJGI. The function of the moxJ gene product is not yet known. MoxG codes for a cytochrome c551i, which functions as the electron acceptor of methanol dehydrogenase. Both methanol dehydrogenase and methylamine dehydrogenase contain PQQ as a cofactor. These so-called quinoproteins are able to catalyze redox reactions by one-electron steps. The reaction mechanism of this oxidation will be described. Electrons from the oxidation reaction are donated to the electron transport chain at the level of cytochrome c. P. denitrificans is able to synthesize at least 10 different c-type cytochromes. Five could be detected in the periplasm and five have been found in the cytoplasmic membrane. The membrane-bound cytochrome c1 and cytochrome c552 and the periplasmic-located cytochrome c550 are present under all tested growth conditions. The cytochromes c551i and c553i, present in the periplasm, are only induced in cells grown on methanol, methylamine, or choline. The other c-type cytochromes are mainly detected either under oxygen limited conditions or under anaerobic conditions with nitrate as electron acceptor or under both conditions. An overview including the induction pattern of all P. denitrificans c-type cytochromes will be given. The genes encoding cytochrome c1, cytochrome c550, cytochrome c551i, and cytochrome c553i have been isolated and sequenced. By using site-directed mutagenesis these genes were mutated in the genome. The mutants thus obtained were used to study electron transport during growth on C1 compounds. This electron transport has also been studied by determining electron transfer rates in in vitro experiments. The exact pathways, however, are not yet fully understood. Electrons from methanol dehydrogenase are donated to cytochrome c551i. Further electron transport is either via cytochrome c550 or cytochrome c553i to cytochrome aa3. However, direct electron transport from cytochrome c551i to the terminal oxidase might be possible as well.(ABSTRACT TRUNCATED AT 400 WORDS)
反硝化副球菌能够利用C1化合物甲醇和甲胺生长。这些化合物被氧化成甲醛，随后甲醛通过甲酸进一步氧化成二氧化碳。通过核酮糖二磷酸途径固定二氧化碳来产生生物质。第一个氧化反应分别由甲醇脱氢酶和甲胺脱氢酶催化。这两种酶均含有α2β2构型的两个不同亚基。编码甲醇脱氢酶亚基的基因（moxF和moxI）已被分离和测序。它们与另外两个基因（moxJ和moxG）位于一个操纵子中，基因顺序为moxFJGI。moxJ基因产物的功能尚不清楚。MoxG编码一种细胞色素c551i，它作为甲醇脱氢酶的电子受体。甲醇脱氢酶和甲胺脱氢酶都含有PQQ作为辅因子。这些所谓的醌蛋白能够通过单电子步骤催化氧化还原反应。将描述这种氧化的反应机制。氧化反应产生的电子在细胞色素c水平上被传递到电子传递链。反硝化副球菌能够合成至少10种不同的c型细胞色素。在周质中可检测到5种，在细胞质膜中发现了5种。膜结合的细胞色素c1和细胞色素c552以及位于周质的细胞色素c550在所有测试的生长条件下都存在。存在于周质中的细胞色素c551i和c553i仅在以甲醇、甲胺或胆碱为碳源生长的细胞中被诱导。其他c型细胞色素主要在氧气受限条件下或在以硝酸盐作为电子受体的厌氧条件下或在这两种条件下被检测到。将给出包括所有反硝化副球菌c型细胞色素诱导模式的概述。编码细胞色素c1、细胞色素c550、细胞色素c551i和细胞色素c553i的基因已被分离和测序。通过使用定点诱变，这些基因在基因组中发生了突变。由此获得的突变体用于研究在C1化合物上生长期间的电子传递。也通过在体外实验中测定电子转移速率来研究这种电子传递。然而，确切的途径尚未完全了解。来自甲醇脱氢酶的电子被传递给细胞色素c551i。进一步的电子传递要么通过细胞色素c550要么通过细胞色素c553i传递给细胞色素aa3。然而，从细胞色素c551i到末端氧化酶的直接电子传递也可能是可行的。（摘要截取自400字）
