Spectroscopic Evidence for a Heme-Heme Binuclear Center in the Cytochrome bd Ubiquinol Oxidase from Escherichia coli
The cytochrome bd complex is a ubiquinol oxidase, which is part of the aerobic respiratory chain of Escherichia coli. This enzyme is structurally unrelated to the heme-Cu oxidases such as cytochrome c oxidase. While the cytochrome bd complex contains no copper, it does have three heme prosthetic gro...
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Published in | Proceedings of the National Academy of Sciences - PNAS Vol. 90; no. 12; pp. 5863 - 5867 |
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Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
Washington, DC
National Academy of Sciences of the United States of America
15.06.1993
National Acad Sciences National Academy of Sciences |
Subjects | |
Online Access | Get full text |
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Summary: | The cytochrome bd complex is a ubiquinol oxidase, which is part of the aerobic respiratory chain of Escherichia coli. This enzyme is structurally unrelated to the heme-Cu oxidases such as cytochrome c oxidase. While the cytochrome bd complex contains no copper, it does have three heme prosthetic groups: heme b558, heme b595, and heme d (a chlorin). Heme b558appears to be involved in the oxidation of quinol, and heme d is known to be the site where oxygen binds and is reduced to water. The role of heme b595, which is high spin, is not known. In this paper, CO is used to probe the oxygen-binding site by use of Fourier transform infrared spectroscopy to monitor the stretching frequency of CO bound to the enzyme. Photodissociation at low temperature (e.g., 20 K) of the CO-heme d adduct results in CO associated with the protein within the heme binding pocket. This photodissociated CO can subsequently relax to form a kinetically trapped CO-heme b595adduct. The data clearly show that heme d and heme b595must reside within a common binding pocket in the enzyme. The catalytic active site where oxygen is reduced to water is, thus, properly considered to be a heme d-heme b595binuclear center. This is analogous to the heme a3-CuBbinuclear center in the heme-Cu oxidases. Heme b595may play roles analogous to those proposed for the CuBcomponent of cytochrome c oxidase. |
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Bibliography: | ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23 ObjectType-Article-1 ObjectType-Feature-2 |
ISSN: | 0027-8424 1091-6490 |
DOI: | 10.1073/pnas.90.12.5863 |