Yoshikawa S, Shinzawa-Itoh K, Tsukihara T
Department of Life Science, Himeji Institute of Technology, Kamigohri, Akoh Hyogo, Japan.
J Bioenerg Biomembr. 1998 Feb;30(1):7-14. doi: 10.1023/a:1020595108560.
Thirteen different polypeptide subunits, each in one copy, five phosphatidyl ethanolamines and three phosphatidyl glycerols, two hemes A, three Cu ions, one Mg ion, and one Zn ion are detectable in the crystal structure of bovine heart cytochrome c oxidase in the fully oxidized form at 2.8 A resolution. A propionate of hems a, a peptide unit (-CO-NH-), and an imidazole bound to CuA are hydrogen-bonded sequentially, giving a facile electron transfer path from CUA to heme a. The O2 binding and reduction site, heme a3, is 4.7 A apart from CuB. Two possible proton transfer paths from the matrix side to the cytosolic side are located in subunit I, including hydrogen bonds and internal cavities likely to contain randomly oriented water molecules. Neither path includes the O2 reduction site. The O2 reduction site has a proton transfer path from the matrix side possibly for protons for producing water. The coordination geometry of CuB and the location of Tyr244 in subunit I at the end of the scalar proton path suggests a hydroperoxo species as the two electron reduced intermediate in the O2 reduction process.
在分辨率为2.8埃的完全氧化形式的牛心细胞色素c氧化酶晶体结构中，可检测到13种不同的多肽亚基，各1个拷贝，5个磷脂酰乙醇胺和3个磷脂酰甘油，2个血红素A，3个铜离子，1个镁离子和1个锌离子。血红素a的一个丙酸酯、一个肽单元（-CO-NH-）和一个与CuA结合的咪唑依次形成氢键，形成了一条从CUA到血红素a的便捷电子传递路径。氧气结合和还原位点血红素a3与CuB相距4.7埃。从基质侧到胞质侧的两条可能的质子传递路径位于亚基I中，包括氢键和可能含有随机取向水分子的内腔。两条路径均不包括氧气还原位点。氧气还原位点有一条从基质侧的质子传递路径，可能用于产生水的质子。CuB的配位几何结构以及亚基I中Tyr244在标量质子路径末端的位置表明，在氧气还原过程中，一种氢过氧物种是双电子还原中间体。
