Requimte-CQFB, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus Caparica, 2829-516 Caparica, Portugal.
Bioinorg Chem Appl. 2012;2012:298739. doi: 10.1155/2012/298739. Epub 2012 Jul 31.
The bacterium Geobacter sulfurreducens (Gs) can grow in the presence of extracellular terminal acceptors, a property that is currently explored to harvest electricity from aquatic sediments and waste organic matter into microbial fuel cells. A family composed of five triheme cytochromes (PpcA-E) was identified in Gs. These cytochromes play a crucial role by bridging the electron transfer from oxidation of cytoplasmic donors to the cell exterior and assisting the reduction of extracellular terminal acceptors. The detailed thermodynamic characterization of such proteins showed that PpcA and PpcD have an important redox-Bohr effect that might implicate these proteins in the e(-)/H(+) coupling mechanisms to sustain cellular growth. The physiological relevance of the redox-Bohr effect in these proteins was studied by determining the fractional contribution of each individual redox-microstate at different pH values. For both proteins, oxidation progresses from a particular protonated microstate to a particular deprotonated one, over specific pH ranges. The preferred e(-)/H(+) transfer pathway established by the selected microstates indicates that both proteins are functionally designed to couple e(-)/H(+) transfer at the physiological pH range for cellular growth.
脱硫杆菌(Gs)能够在存在细胞外末端受体的情况下生长,目前正在探索利用这一特性从水生沉积物和有机废物中获取电能,将其转化为微生物燃料电池。Gs 中鉴定出一个由五个三血红素细胞色素(PpcA-E)组成的家族。这些细胞色素通过桥接从细胞质供体氧化到细胞外部的电子转移,并协助细胞外末端受体的还原,从而发挥关键作用。对这些蛋白质的详细热力学特性进行了表征,结果表明 PpcA 和 PpcD 具有重要的氧化还原-Bohr 效应,这可能暗示这些蛋白质参与了 e(-)/H(+)偶联机制,以维持细胞生长。通过在不同 pH 值下确定每个单独的氧化还原微观状态的分数贡献,研究了这些蛋白质中氧化还原-Bohr 效应的生理相关性。对于这两种蛋白质,氧化过程都从特定的质子化微观状态到特定的去质子化微观状态进行,跨越特定的 pH 范围。所选微观状态确定的优选 e(-)/H(+)转移途径表明,这两种蛋白质在细胞生长的生理 pH 范围内,在功能上都被设计为偶联 e(-)/H(+)转移。