S. Yoshikawa et al., CRYSTAL-STRUCTURE OF BOVINE HEART CYTOCHROME-C-OXIDASE AT 2.8 ANGSTROM RESOLUTION, Journal of bioenergetics and biomembranes, 30(1), 1998, pp. 7-14
Thirteen different polypeptide subunits, each in one copy, five phosph
atidyl ethanolamines and three phosphatidyl glycerols, two hemes A, th
ree 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 f
orm at 2.8 Angstrom resolution. A propionate of hems a, a peptide unit
(-CO-NH-), and an imidazole bound to Cu-A are hydrogen-bonded sequent
ially, giving a facile electron transfer path from Cu-A to heme a. The
O-2 binding and reduction site, heme a(3), is 4.7 Angstrom apart from
Cu-B. 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 O-2 reduction site. The O-2 reduction site
has a proton transfer path from the matrix side possibly for protons f
or producing water. The coordination geometry of Cu-B and the location
of Tyr(244) in subunit I at the end of the scalar proton path suggest
s a hydroperoxo species as the two electron reduced intermediate in th
e O-2 reduction process.