Kirichenko A, Vygodina T, Mkrtchyan H M, Konstantinov A
A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Russia.
FEBS Lett. 1998 Feb 27;423(3):329-33. doi: 10.1016/s0014-5793(98)00117-3.
Calcium ion binds reversibly with cytochrome c oxidase from beef heart mitochondria (Kd approximately 2 microM) shifting alpha- and gamma-absorption bands of heme a to the red. Two sodium ions compete with one Ca2+ for the binding site with an average dissociation constant square root[K1(Na) x K2(Na)] approximately 3.6 mM. The Ca2+-induced spectral shift of heme a is specific for mammalian cytochrome c oxidase and is not observed in bacterial or yeast aa3 oxidases although the Ca2+-binding site has been revealed in the bacterial enzyme [Ostermeier, C., Harrenga, A., Ermler, U. and Michel, H. (1997) Proc. Natl. Acad. Sci. USA 94, 10547-10553]. As His-59 and Gln-63 involved in Ca2+ binding with Subunit I of P. denitrificans oxidase are not conserved in bovine oxidase, these residues have to be substituted by alternative ligands in mammalian enzyme, which is indeed the case as shown by refined structure of bovine heart cytochrome oxidase (S. Yoshikawa, personal communication). We propose that it is interaction of Ca2+ with the species-specific ligand(s) in bovine oxidase that accounts for perturbation of heme a. The Ca2+/Na2+-binding site may be functionally associated with the exit part of 'pore B' proton channel in subunit I of mammalian cytochrome c oxidase.
钙离子与牛心线粒体细胞色素c氧化酶可逆结合（解离常数Kd约为2微摩尔），使血红素a的α和γ吸收带向红色移动。两个钠离子与一个Ca2+竞争结合位点，平均解离常数平方根[K1(Na)×K2(Na)]约为3.6毫摩尔。Ca2+诱导的血红素a光谱位移是哺乳动物细胞色素c氧化酶特有的，在细菌或酵母aa3氧化酶中未观察到，尽管在细菌酶中已揭示了Ca2+结合位点[奥斯特迈尔，C.，哈伦加，A.，埃尔默勒，U.和米歇尔，H.（1997年）《美国国家科学院院刊》94，10547 - 10553]。由于参与反硝化假单胞菌氧化酶亚基I与Ca2+结合的组氨酸-59和谷氨酰胺-63在牛氧化酶中不保守，这些残基在哺乳动物酶中必须被替代配体取代，牛心脏细胞色素氧化酶的精细结构所示情况确实如此（吉川，S.，个人交流）。我们提出，正是Ca2+与牛氧化酶中物种特异性配体的相互作用导致了血红素a的扰动。Ca2+/Na2+结合位点可能在功能上与哺乳动物细胞色素c氧化酶亚基I中“孔B”质子通道的出口部分相关联。
