Effect of Membrane Environment on Ligand-Binding Properties of the Terminal Oxidase Cytochrome bd-I from Escherichia coliстатья
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Дата последнего поиска статьи во внешних источниках: 20 января 2021 г.
Аннотация:Cytochrome bd-I is a terminal oxidase of the Escherichia coli respiratory chain. This integral membrane protein contains three redox-active prosthetic groups: hemes b558, b595, and d. The enzyme couples the electron transfer from quinol to molecular oxygen to proton-motive force generation and carries out important physiological functions. The study aimed at examining the effect of the membrane environment on ligand-binding properties of cytochrome bd-I. For this purpose, absorption spectroscopy was used. The membrane environment was found to modulate the ligand-binding characteristics of the hemoprotein in both the oxidized and reduced state. Absorption changes observed upon the addition of an exogenous ligand, such as cyanide or carbon monoxide (CO), to the detergent-solubilized enzyme are much more extensive and heterogeneous than those with the membranes. In the native membranes both cyanide and CO interact mainly with heme d. When the enzyme is isolated, an additional ligand-binding site (heme b558) appears as evidenced by increased absorption changes in the Soret band. This additional reactivity can also be detected upon a simple treatment of the membranes with detergent. The effect is not a trivial denaturation since the reconstitution of the isolated enzyme into azolectin liposomes restores the ligand-binding pattern close to that of the intact membranes.