Wakatsuki T
Department of Biochemistry, Kyoto Pharmaceutical University, Japan.
J Ind Microbiol. 1995 Feb;14(2):169-77. doi: 10.1007/BF01569900.
For many organisms, some heavy metals in external media are essential at low concentrations but are toxic at high concentrations. Strongly toxic heavy metals are toxic even at low concentrations. Recently, it was proven that changes of valencies of Fe, Cu and Mn were necessary for these metals to be utilized by organisms, especially microorganism. The valencies of Hg and Cr are changed by reducing systems of cells in the process of detoxifying them. Thus, the processes of oxidoreduction of these metals are important for biological systems of metal-autoregulation and metal-mediated regulation. Metal ion-specific reducing enzyme systems function in the cell surface layer of microorganisms. These enzymes require NADH or NADPH as an electron donor and FMN or FAD as an electron carrier component. Electron transport may be operated by transplamsa-membrane redox systems. Metal ion reductases are also found in the cytoplasm. The affinities of metal ions to ligand residues change with the valence of the metal elements and mutual interactions of various metal ions are important for regulation of oxidoreduction states. Microorganisms can utilize essential metal elements and detoxify excess metals by respective reducing enzyme systems and by regulating movement of heavy metal ions.
对于许多生物体而言，外部介质中的某些重金属在低浓度时是必需的，但在高浓度时则具有毒性。剧毒重金属即使在低浓度下也具有毒性。最近，已证明铁、铜和锰的价态变化对于这些金属被生物体尤其是微生物利用是必要的。汞和铬的价态在细胞解毒过程中通过细胞的还原系统发生变化。因此，这些金属的氧化还原过程对于金属自动调节和金属介导调节的生物系统很重要。金属离子特异性还原酶系统在微生物的细胞表层发挥作用。这些酶需要NADH或NADPH作为电子供体，FMN或FAD作为电子载体成分。电子传递可能由跨质膜氧化还原系统进行操作。金属离子还原酶也存在于细胞质中。金属离子与配体残基的亲和力随金属元素的价态而变化，各种金属离子之间的相互作用对于氧化还原状态的调节很重要。微生物可以通过各自的还原酶系统以及通过调节重金属离子的移动来利用必需的金属元素并使过量的金属解毒。
