Examination of the role of subunits and lipids in cytochrome c oxidase based on x-ray crystallographic structure

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Cytochrome c oxidase, the terminal enzyme of the respiratoly chain, contains a variable number of the subunits depending on the evolutionry stage of the organism. The Paracoccus denitrificans enzymes contain three subunits, which are homologous to three mitochondrial-encoded subunits of the eukaryotic enzyme. The yeast enzymes contain additional eight nuclear-encoded subunits, the mammalian enzymes contain ten subunits. The crystal structure of bovine heart cytochrome c oxidase at 2.8 A resolution reveals eight phospholipids in this enzyme. All of thses enzyme catalize essentially same reaction in spite of the differences of the compornents. the aim of the present study is examination of the role of the additional subunits, lipids and metals from both the structures and functions. The p.denitrificas enzyme, composed of 2 subunits, was purified and crystalized. But, the collection of data was not succeeded because of the sensitivity to X-ray irradiation. Crystallization conditions of bovine heart enzyme have been improved to provide crystals which diffract x-rays up to 1.9A resolution, and the crystal structures of this enzyme were determined at 2.3A resolution. This structure reveled Na/Na site, Mg site and Zn site in addition to two hemes a and three cuppers. The composition and Structure of the phosholipids in the crystalline preparation were determined with mass spectrometry. PC,RE,PG and CL were assingned from the chromatographic pattern as well as the mass spectrometry. The MAS-MAS analysis indicate that structure of fatty acids of each phospholipids are fairly unique.