Korszun Z R, Salemme F R
Proc Natl Acad Sci U S A. 1977 Dec;74(12):5244-7. doi: 10.1073/pnas.74.12.5244.
Cytochrome c555 is an 86-residue type c cytochrome derived from Chlorobium thiosulfatophilum, an obligately anaerobic green sulfur bacterium which is among the most primitive of living organisms. Here is presented a preliminary structural description of the cytochrome c555 molecule based on its crystallographic structure determination at 2.7-A resolution by multiple isomorphous replacement methods. This structure is of interest not only because of its evolutionary significance but also because the cytochrome c555 molecule possesses an unusually low physiologic oxidoreduction potential (Em,7 = +145 mV) compared with related members of the cytochrome c family. Consequently, determination of its structure may permit a direct assessment of the structural factors responsible for prosthetic group redox potential regulation in type c cytochromes.
细胞色素c555是一种由嗜硫绿菌属的嗜硫绿菌衍生而来的含86个氨基酸残基的c型细胞色素，嗜硫绿菌是一种专性厌氧绿色硫细菌，属于最原始的生物体之一。本文基于通过多同晶置换法在2.7埃分辨率下对其晶体结构的测定，给出了细胞色素c555分子的初步结构描述。该结构之所以令人感兴趣，不仅是因为其进化意义，还因为与细胞色素c家族的相关成员相比，细胞色素c555分子具有异常低的生理氧化还原电位（Em,7 = +145 mV）。因此，对其结构的测定可能有助于直接评估负责c型细胞色素中辅基氧化还原电位调节的结构因素。
