Trofimov A A, Polyakov K M, Lazarenko V A, Popov A N, Tikhonova T V, Tikhonov A V, Popov V O
Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, ul. Vavilova 32, Moscow 119991, Russian Federation.
European Synchrotron Radiation Facility, BP-220, 38043 Grenoble, France.
Acta Crystallogr D Biol Crystallogr. 2015 May;71(Pt 5):1087-94. doi: 10.1107/S1399004715003053. Epub 2015 Apr 24.
Octahaem cytochrome c nitrite reductase from the bacterium Thioalkalivibrio nitratireducens catalyzes the reduction of nitrite to ammonium and of sulfite to sulfide. The reducing properties of X-ray radiation and the high quality of the enzyme crystals allow study of the catalytic reaction of cytochrome c nitrite reductase directly in a crystal of the enzyme, with the reaction being induced by X-rays. Series of diffraction data sets with increasing absorbed dose were collected from crystals of the free form of the enzyme and its complexes with nitrite and sulfite. The corresponding structures revealed gradual changes associated with the reduction of the catalytic haems by X-rays. In the case of the nitrite complex the conversion of the nitrite ions bound in the active sites to NO species was observed, which is the beginning of the catalytic reaction. For the free form, an increase in the distance between the oxygen ligand bound to the catalytic haem and the iron ion of the haem took place. In the case of the sulfite complex no enzymatic reaction was detected, but there were changes in the arrangement of the active-site water molecules that were presumably associated with a change in the protonation state of the sulfite ions.
来自嗜碱硝酸还原硫杆菌的八聚体细胞色素c亚硝酸盐还原酶催化亚硝酸盐还原为铵以及亚硫酸盐还原为硫化物。X射线辐射的还原特性以及酶晶体的高质量使得能够直接在酶晶体中研究细胞色素c亚硝酸盐还原酶的催化反应，该反应由X射线诱导。从游离形式的酶及其与亚硝酸盐和亚硫酸盐的复合物的晶体中收集了一系列随着吸收剂量增加的衍射数据集。相应的结构揭示了与X射线催化血红素还原相关的逐渐变化。在亚硝酸盐复合物的情况下，观察到结合在活性位点的亚硝酸根离子转化为NO物种，这是催化反应的开始。对于游离形式，与催化血红素结合的氧配体与血红素铁离子之间的距离增加。在亚硫酸盐复合物的情况下，未检测到酶促反应，但活性位点水分子的排列发生了变化，这可能与亚硫酸根离子的质子化状态变化有关。
