Myers J M, Myers C R
Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee, WI 53226, USA.
Lett Appl Microbiol. 2003;37(1):21-5. doi: 10.1046/j.1472-765x.2003.01338.x.
To determine if the outer membrane (OM) cytochromes OmcA and OmcB of the metal-reducing bacterium Shewanella oneidensis MR-1 have distinct or overlapping roles in the reduction of insoluble manganese(IV) oxide.
The gene replacement mutant (OMCA1) which lacks OmcA was partially deficient in Mn(IV) reduction. Complementation of OMCA1 with a vector (pVK21) that contains omcB but not omcA restored Mn(IV) reduction to levels that were even greater than those of wild-type. Examination of the OM of OMCA1/pVK21 revealed greater than wild-type levels of OmcB protein and specific haem content.
Overexpression of OmcB can compensate for the absence of OmcA in the reduction of insoluble Mn(IV) oxides. Therefore, there is at least a partial overlap in the roles of these OM cytochromes in the reduction of insoluble Mn(IV) oxide.
The overlapping roles of these two cytochromes has important implications for understanding the mechanism by which MR-1 reduces insoluble metal oxides. There is no obligatory sequential electron transfer from one cytochrome to the other. They could both potentially serve as terminal reductases for extracellular electron acceptors.
确定金属还原菌——希瓦氏菌属MR - 1的外膜（OM）细胞色素OmcA和OmcB在还原不溶性锰（IV）氧化物过程中是具有不同作用还是重叠作用。
缺乏OmcA的基因替代突变体（OMCA1）在锰（IV）还原方面存在部分缺陷。用含有omcB但不含omcA的载体（pVK21）对OMCA1进行互补，可使锰（IV）还原恢复到甚至高于野生型的水平。对OMCA1/pVK21的外膜检查发现，OmcB蛋白和特定血红素含量高于野生型水平。
在还原不溶性锰（IV）氧化物过程中，OmcB的过表达可以弥补OmcA的缺失。因此，这些外膜细胞色素在还原不溶性锰（IV）氧化物中的作用至少存在部分重叠。
这两种细胞色素的重叠作用对于理解MR - 1还原不溶性金属氧化物的机制具有重要意义。不存在从一种细胞色素到另一种细胞色素的强制性顺序电子转移。它们都有可能作为细胞外电子受体的末端还原酶。
