Abstract
Carbon monoxide bound to cytochrome c oxidase has been observed by Fourier transform infrared spectroscopy between 10 K and 280 K in the dark and during and after continuous photolysis. CO bound to a3Fe absorbs near 1963 cm-1, with minor bands at lower frequencies. Photolysis at low temperatures transfers CO to CuB, with the major component near 2062 cm-1 and a minor one near 2043 cm-1. Vibrational absorptions are assigned by comparison with heme and copper carbonyls, by frequency dependence of all bands on the isotopic mass of CO, and by similar behavior of major and minor components with photolysis and relaxation kinetics as a function of temperature. Reformation of a3FeCO after photolysis is an apparent first order process below 210 K with a distribution of rate constants. The kinetics are well described by a power law. Arrhenius behavior is followed between 140 K and 180 K to yield a peak activation enthalpy of 40.3 kJ/mol and a distribution in g(H) = 2.56 kJ/mol (full width at half-maximum). The major component of a3FeCO shows a very narrow CO absorption band (full width at half-maximum = 2.4 cm-1), while that of CuBCO shows a broader CO absorption (full width at half-maximum = 6 cm-1). These data indicate that in the reduced carbon monoxide complex, a3FeCO is in highly ordered nonpolar surroundings sufficiently separated from CuB that it is not perturbed by motion of the latter, while CuBCO is in less ordered, more flexible surroundings.
Highlights
Carbon monoxide bound to cytochromec oxidase has tioned metal sitescontribute to thevisible spectra, while the been observed by Fourier transform infraredspectros- possible contributions from the second copper (EPR silent, copy between 10 K and 280 K in the dark and during CUB)have been unclear [2]. and after continuous photolysis
The major component of a8eCO shows a studied by effects on cytochrome a3 absorption spectra near very narrow CO absorption band (full width at half- 430 nm and 590 nm [7,8,9,10].Analysis of low temperature maximum = 2.4 cm"), while that ofCUBCO shows a recombination kinetics led Sharrock and Yonetani [7] to broader CO absorption
These data indicate that in thereduced carbon species contained only one CO molecule. monoxide complex, aFeCO is in highly ordered non- Identification of this site for photolyzed CO as the CUBCO polarsurroundings sufficiently separated from CUB complex wasrecently reported by Alben et al [11, 12]by use that it isnot perturbed by motion of the latter, while of FTIR spectroscopy
Summary
Ment for the FeCO of the main enzyme species. The CuCO We previously reported [11, 12] the vibrational absorption complexes are in a more polar and flexible environment than spectrum of carbon monoxide coordinated to cytochrome u3 is the main heme component. Heme (asFeCO) and its low temperature photolysis product which was assignedto Cu&O by comparison with vibrational
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