Molina-Heredia Fernando P, Balme Alexis, Hervás Manuel, Navarro José A, De la Rosa Miguel A
Instituto de Bioquímica Vegetal y Fotosíntesis, Centro Isla de la Cartuja, Universidad de Sevilla y CSIC, Américo Vespucio s/n, Sevilla, Spain.
FEBS Lett. 2002 Apr 24;517(1-3):50-4. doi: 10.1016/s0014-5793(02)02576-0.
Cytochrome cM is a new c-class photosynthetic haem protein whose physiological role is still unknown. It has been proposed previously that cytochrome cM can replace cytochrome c6 and plastocyanin in transferring electrons between the two membrane complexes cytochrome b6-f and photosystem I in organisms growing under stress conditions. The experimental evidence herein provided allows us to discard such a hypothesis. We report a procedure to overexpress cytochrome cM from the cyanobacterium Synechocystis sp. PCC 6803 in Escherichia coli cells in mg quantities. This has allowed us to perform a comparative laser flash-induced kinetic analysis of photosystem I reduction by the three metalloproteins from Synechocystis. The bimolecular rate constant for the overall reaction is up to 100 times lower with cytochrome cM than with cytochrome c6 or plastocyanin. In addition, the redox potential value and surface electrostatic potential distribution of cytochrome cM are quite different from those of cytochrome c6 and plastocyanin. These findings strongly indicate that cytochrome cM cannot be recognised by and interact with the same redox partners as the other two metalloproteins.
细胞色素cM是一种新型的c类光合血红素蛋白，其生理作用尚不清楚。此前有人提出，在胁迫条件下生长的生物体中，细胞色素cM可以在细胞色素b6-f和光系统I这两个膜复合物之间传递电子时替代细胞色素c6和质体蓝素。本文提供的实验证据使我们能够摒弃这一假设。我们报告了一种在大肠杆菌细胞中大量过量表达来自集胞藻属PCC 6803蓝细菌的细胞色素cM的方法。这使我们能够对集胞藻属的三种金属蛋白还原光系统I进行比较性的激光闪光诱导动力学分析。细胞色素cM参与的整个反应的双分子速率常数比细胞色素c6或质体蓝素低多达100倍。此外，细胞色素cM的氧化还原电位值和表面静电势分布与细胞色素c6和质体蓝素的截然不同。这些发现有力地表明，细胞色素cM无法被其他两种金属蛋白识别，也不能与它们的氧化还原伙伴相互作用。
