X-ray crystallographic studies on molecular mechanism of Oxygen respriration

测定了牛心脏细胞色素c氧化酶在不同状态下的晶体结构。2.3*分辨率为完全氧化态；完全还原态，2.35*；CO结合完全还原态，2.8*；叠氮化物结合完全氧化态，2.9*。在2.3*分辨率下对完全氧化酶的晶体结构分析表明：(1)一个过氧化物基团桥接Fea3和CuB双核中心作为氧还原位点，(2)CuB配体之一His240和Tyr244通过共价键连接，(3)存在促进电子和质子转移的水分子，(4)Na或Ca离子位于酶分子内，(5)酶形成由心磷脂分子稳定的二聚体结构。(6)跨膜a-螺旋在甘氨酸残基中含量丰富，约占7%，不会断裂a-螺旋。全还原酶在2.35*分辨率下的晶体结构分析表明：(1)氧还原位点不存在配体，(2)还原态I亚基Gly49到Asn55的残基构象与氧化态不同。在2.8*分辨率下对CO结合的全还原酶进行晶体结构分析，发现(1)CO基团连接Fea3， (2) I亚基的Gly49 ~ Asn55残基的构象与还原态相似。在2.9*分辨率下对叠氮化物结合氧化形式的晶体结构分析表明：(1)叠氮化物基团结合在氧还原位点和酶的分子表面，(2)与CuB连接的所有组氨酸残基与细菌酶相比没有多重构象状态。

Crystal structures of cytochome c oxidase from bovine heart at various states are determined. Fully oxidized state was at 2.3*resolution ; fully reduced state, 2.35* ; CO bound fully reduced state, 2.8* ; azide bound fully oxidized state, 2.9*.Crystal structure analysis of the fully oxidized enzyme at 2.3* resolution revealed that (1) a peroxide group bridges Fea3 and CuB dinuclear center which is an oxygen reduction site, (2) His240, one of the ligands of CuB,and Tyr244 are linked by a covalent bond, (3) there exist water molecules contributing electron and proton transfer, (4) Na or Ca ions are located within the enzyme melecule, (5) the enzyme forms dimeric structure stabilized by cardiolipin molecules, (6) trans-membrane a-helices are abundant in glycine residues at 7%, which do not break a-helices.Crystal structure analysis of fully reduced enzyme at 2.35* resolution elucidated that (1) the oxygen reduction site has no ligand, (2) the residues fro Gly49 to Asn55 of subunit I in reduced state are different from those in oxidized state in their conformation.Crystal structure analysis of the CO bound fully reduced enzyme at 2.8* resolution revealed that (1) CO group ligates Fea3, and (2) the residues Gly49 to Asn55 of subunit I are similar to those of the reduced state in their conformation.Crystal structure analysis of the azide bound oxidized form at 2.9* resolution revealed that (1) azide groups bound at the oxygen reduction site and a molecular surface of the enzyme, and (2) all the histidine residues which ligate to the CuB do not have multiple conformational states in contrast to those of the bacterial enzyme.