The cytochromes ofEscherichia coli

Abstract

Escherichia coli contains numerous heme‐containing proteins when grown either aerobicaly or anaerobically. These cytochrome species are distributed in the cytoplasm, the periplasm, or are bound to the cytoplasmic membrane. They are involved in various physiological functions, including electron transport, oxidative phosphorylation, assimilatory metabolism and detoxification. One dozen unique cytochrome species have been biochemically and/or genetically characterized. They contain one or more of the four heme groups which E. coli is known to produce: protoheme IX, heme c, heme d, and siroheme. The purpose of this articles is to summarize what we know about the structure and function of this collection of heme proteins.

Preparation and Initial Characterization of the Compound I, II, and III States of Iron Methylchlorin-Reconstituted Horseradish Peroxidase and Myoglobin: Models for Key Intermediates in Iron Chlorin Enzymes

“…E. coli cytochrome cd, the predominant terminal oxidase under low oxygen conditions, contains two iron protohemes and an iron transdihydroxychlorin (heme d), with the latter being the primary ligand binding site that binds oxygen strongly (10,11). The enzyme is isolated mainly in the oxyferrous state (5). A reaction cycle including oxyferrous and oxoferryl intermediates has been proposed (10,11).…”

“…Nature employs reduced porphyrin prosthetic groups such as chlorins (1) in catalases from E. coli (HPII) (2,3) and N. crassa (4), terminal oxidases from E. coli (5), sulfite and nitrite reductases (6), and sulfmyoglobin (7). Typically green in color, such proteins have spectral properties that differ significantly from heme proteins with fully conjugated iron porphyrins.…”

Site-Directed Mutation of the Highly Conserved Region near the Q-Loop of the Cytochrome bd Quinol Oxidase from Escherichia coli Specifically Perturbs Heme b595

“…Cytochrome bd quinol oxidase is one of two quinol oxidases in the respiratory chain of Escherichia coli () and is expressed under microaerophilic growth conditions ( − ). The enzyme is an integral membrane heterodimer ( , ), and it catalyzes the two-electron oxidation of ubiquinol-8 and the four-electron reduction of dioxygen to water with the release of protons into the periplasmic space and the generation of a protonmotive force ( − ). Cytochrome bd is the only prokaryotic respiratory oxidase that does not belong to the heme−copper oxidase superfamily ( , ) and shows no homology to the members of this superfamily ( , ).…”

Compensations for Diminished Terminal Oxidase Activity in Escherichia coli

“…The aerobic electron transport chain of Escherichia coli contains two well characterized terminal quinol oxidases, cytochrome bd-I and cytochrome boЈ, which are encoded by the cydAB and cyoABCDE operons, respectively (1,2). Additionally, the appBC locus of E. coli has been shown to encode a terminal oxidase of the cytochrome bd type (cytochrome bd-II) (3,4).…”