SPECTROSCOPIC EVIDENCE FOR A HEME HEME BINUCLEAR CENTER IN THE CYTOCHROME BD UBIQUINOL OXIDASE FROM ESCHERICHIA-COLI

被引:113
作者
HILL, JJ
ALBEN, JO
GENNIS, RB
机构
[1] UNIV ILLINOIS,SCH CHEM SCI,505 S MATHEWS AVE,URBANA,IL 61801
[2] OHIO STATE UNIV,DEPT MED BIOCHEM,COLUMBUS,OH 43210
关键词
FOURIER TRANSFORM INFRARED SPECTROSCOPY; FLASH PHOTOLYSIS; PHOTOSELECTION; HEME POCKET; CO STRETCHING VIBRATION;
D O I
10.1073/pnas.90.12.5863
中图分类号
O [数理科学和化学]; P [天文学、地球科学]; Q [生物科学]; N [自然科学总论];
学科分类号
07 ; 0710 ; 09 ;
摘要
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 b558 appears 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 b595 adduct. The data clearly show that heme d and heme b595 must 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 b595 binuclear center. This is analogous to the heme a3-Cu(B) binuclear center in the heme-Cu oxidases. Heme b595 may play roles analogous to those proposed for the Cu(B) component of cytochrome c oxidase.
引用
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页码:5863 / 5867
页数:5
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