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Resonance Raman spectroscopy of the integral quinol oxidase complex of Sulfolobus acidocaldarius
Citation key ISI:A1996VK59400016
Author Gerscher, S and Dopner, S and Hildebrandt, P and Gleissner, M and Schafer, G
Pages 12796-12803
Year 1996
ISSN 0006-2960
Address 1155 16TH ST, NW, WASHINGTON, DC 20036
Journal Biochemistry
Volume 35
Number 39
Month OCT 1
Abstract The integral quinol oxidase complex of Sulfolobus acidocaldorius (DSM 639) was investigated by resonance Raman spectroscopy. The complex includes four heme a groups which constitute two functional entities, a(587) and aa(3), containing two low-spin hemes and a low-spin as well as a high-spin heme, respectively. RR spectra were obtained from the fully oxidized and fully reduced states of the complex using different excitation wavelengths in the Soret band region in order to disentangle the contributions from the four heme groups. For the oxidized state, this approach allowed for the identification of two spectrally different types of heme a which were assigned to the bishistidine ligated hemes a of aa(3) and a(587) (type II) and to the additional heme a of a(587) which is Ligated by a histidine and methionine (type I). The spectra of both heme a types differ substantially from that of beef heart cytochrome c oxidase, In particular, the formyl stretching modes of types II and I are upshifted by 8 and 15 cm(-1), respectively, implying a largely hydrophobic environment of the formyl groups in the quinol oxidase of Sulfolobus. Furthermore, the RR spectra of the oxidized stare reveal the characteristic marker bands of a five-coordinated and a six-coordinated high-spin state, indicating that heme ns exists in a coordination equilibrium, which is in sharp contrast to the purely six-coordinated high-spin configuration of heme a(3) in any (quinol or cytochrome) oxidases studied so far, Also the formyl stretching mode of heme as appears to be unusual as its frequency is substantially lower than in beef heart oxidase. In the fully reduced state, no heterogeneity of heme ns is observed and also the spectra of the various hemes a are nearly indistinguishable. Moreover, the formyl stretching vibrations of all hemes a and as apparently coincide to one prominent peak at 1658 cm(-1) characteristic for a non-hydrogen-bonded carbonyl group. This finding is unique compared to other aa(3) oxidases In which the formyl stretchings give rise to widely separated bands at similar to 1610 and similar to 1665 cm(-1) for heme a and a(3), respectively, In both the oxidized and the reduced states, the spectra of the an, entity in the integral complex differ significantly from those of the isolated aa(3) entity studied previously [Heibel, G., Anzenbacher, P., Hildebrandt, P., & Schafer, G. (1993a) Biochemistry 32, 10878-10884], indicating substantial interactions between the various subunits of the integral complex.
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