The terminal oxidase cytochrome bd-I confers carbon monoxide resistance to Escherichia coli cells

Carbon monoxide (CO) plays a multifaceted role in the physiology of organisms, from poison to signaling molecule. Heme proteins, including terminal oxidases, are plausible CO targets. Three quinol oxidases terminate the branched aerobic respiratory chain of Escherichia coli. These are the heme-copper cytochrome bo3 and two copper-lacking bd-type cytochromes, bd-I and bd-II. All three enzymes generate a proton motive force during the four-electron oxygen reduction reaction that is used for ATP production. The bd-type oxidases also contribute to mechanisms of bacterial defense against various types of stresses. Here we report that in E. coli cells, at the enzyme concentrations tested, cytochrome bd-I is much more resistant to inhibition by CO than cytochrome bd-II and cytochrome bo3. The apparent half-maximal inhibitory concentration values, IC50, for inhibition of O2 consumption of the membrane-bound bd-II and bo3 oxidases by CO at-150 & mu;M O2 were estimated to be 187.1 & PLUSMN; 11.1 and 183.3 & PLUSMN; 13.5 & mu;M CO, respectively. Under the same conditions, the maximum inhibition observed with the membrane-bound cytochrome bd-I was 20 & PLUSMN; 10% at-200 & mu;M CO

Preparations of Terminal Oxidase Cytochrome bd-II Isolated from Escherichia coli Reveal Significant Hydrogen Peroxide Scavenging Activity

Cytochrome bd-II is one of the three terminal quinol oxidases of the aerobic respiratory chain of Escherichia coli. Preparations of the detergent-solubilized untagged bd-II oxidase isolated from the bacterium were shown to scavenge hydrogen peroxide (H2O2) with a high rate with production of molecular oxygen (O2). The addition of H2O2 to the same buffer that does not contain enzyme or contains thermally denatured cytochrome bd-II does not lead to any O2 evolution. The latter observation rules out the involvement of metals adventitiously bound to the protein. The H2O2–induced O2 production is not susceptible to inhibition by N-ethylmaleimide (the sulfhydryl binding compound), antimycin A (the compound that binds specifically to a quinol binding site) and CO (the diatomic gas that binds specifically to the reduced heme d). However, the O2 formation is inhibited by cyanide (IC50 = 4.5 ± 0.5 µM) and azide. The addition of H2O2 in the presence of dithiothreitol and ubiquinone-1 does not inactivate cytochrome bd-II and apparently does not affect the O2 reductase activity of the enzyme. The ability of cytochrome bd-II to detoxify H2O2 could play a role in bacterial physiology by conferring resistance to the peroxide-mediated stress

ROS defense systems and terminal oxidases in bacteria

Reactive oxygen species (ROS) comprise the superoxide anion (O2•-), hydrogen peroxide (H2O2), hydroxyl radical (•OH), and singlet oxygen (1O2). ROS can damage a variety of macromolecules, including DNA, RNA, proteins, and lipids, and compromise cell viability. To prevent or reduce ROS-induced oxidative stress, bacteria utilize different ROS defense mechanisms, of which ROS scavenging enzymes, such as superoxide dismutases, catalases, and peroxidases, are the best characterized. Recently, evidence has been accumulating that some of the terminal oxidases in bacterial respiratory chains may also play a protective role against ROS. The present review covers this role of terminal oxidases in light of recent findings

The Second International Asteroid Warning Network Timing Campaign: 2005 LW3

The Earth close approach of near-Earth asteroid 2005 LW3 on 2022 November 23 represented a good opportunity for a second observing campaign to test the timing accuracy of astrometric observation. With 82 participating stations, the International Asteroid Warning Network collected 1046 observations of 2005 LW3 around the time of the close approach. Compared to the previous timing campaign targeting 2019 XS, some individual observers were able to significantly improve the accuracy of their reported observation times. In particular, U.S. surveys achieved good timing performance. However, no broad, systematic improvement was achieved compared to the previous campaign, with an overall negative bias persisting among the different observers. The calibration of observing times and the mitigation of timing errors should be important future considerations for observers and orbit computers, respectively.Funder: Institute of Cosmos SciencesUniversity of Barcelona (CEX2019-000918-M); European Union (PID2021-122842OB-C21);Full text license: CC BY</p