Some magnetic properties of Pseudomonas cytochrome oxidase

Abstract

The magnetic properties of the haem groups of Pseudomonas cytochrome oxidase and its cyanide-bound derivatives were studied in both the oxidized and reduced states by means of m.c.d. (magnetic circular dichroism) at low temperatures. In addition, the oxidized forms of the enzyme were also investigated by e.p.r. (electron-paramagnetic-resonance) spectroscopy, and a parallel study, using both e.p.r. and m.c.d., was made on Pseudomonas cytochrome c-551 to aid spectral assignments. For ascorbate-reduced Pseudomonas cytochrome oxidase, the temperature-independence of those features in the m.c.d. spectrum corresponding to the haem c, and the temperature-dependence of those signals corresponding to the haem d1, showed the former to be low-spin and the latter to be high-spin (s = 2). However, addition of cyanide to the reduced enzyme gave a form of the protein that was completely low-spin. The e.p.r. and m.c.d. sectra of oxidized Pseudomonas cytochrome oxidase and its cyanide derivative were consistent with the haem c and d1 components being low-spin in both cases. Pseudomonas cytochrome c-551 was found to be low-spin in both its oxidized and reduced redox states.

Resonance Raman spectra of heme c and heme d1 in Pseudomonas cytochrome oxidase

“…Its presence in the Pseudomonas cytochrome oxidase spectrum is thus consistent with 5-coordination with an imidazole ligand. Upon cyanide binding and conversion to a 6-coordinate, low-spin configuration [18], these low frequency modes disappear in a manner analogous to the spectral behavior observed upon 02 binding to hemoglobin.…”

“…However, this heme c/heme dl electronic interaction was called into question by a reappraisal of the MCD spectroscopic results [21]. Due to the clear separation between the 2 types of heme by selective laser excitation, we have been able to examine the heme c spectra in the absence or presence of cyanide bound to the heme d~, conditions under which the heme dl undergoes a high-low-spin transition [ 18 ]. In contrast to the pronounced spectral changes detected in the heme dl upon binding cyanide, the Raman spectrum of the heme c is not significantly affected.…”

Y25S Variant of Paracoccus pantotrophus Cytochrome cd1 Provides Insight into Anion Binding by d1 Heme and a Rare Example of a Critical Difference between Solution and Crystal Structures

“…It can now be proposed that an oxidized c heme Söret band of a cytochrome cd 1 at 410 -411 nm is a strong indication of His/ Met coordination at the c heme for cytochrome cd 1 . When oxidized P. aeruginosa cytochrome cd 1 was mixed with imidazole, the c heme Söret band shifted from 411 to 406 nm (28), reflecting the displacement of methionine by imidazoles; this extends the proposal to include a 406 nm c heme Söret band as an indication of His/His coordination. Erythrobacter sp.…”

“…This would not usually be cause to doubt a 1.4 Å crystal structure, although the Y25S cytochrome cd 1 crystal structure surprisingly showed no difference in c heme ligation or ligand orientation from the wild type. The visible absorbance c heme Söret bands of the oxidized wild type cytochromes cd 1 from P. aeruginosa and P. stutzeri both lie at 411 nm (2,27). It can now be proposed that an oxidized c heme Söret band of a cytochrome cd 1 at 410 -411 nm is a strong indication of His/ Met coordination at the c heme for cytochrome cd 1 .…”

Resonance Raman and surface‐enhanced resonance Raman studies of cytochrome cd1

“…The native enzyme is a dimer composed of two identical subunits each of which is -60 000 Mr and contains one c-type and one d,-type heme [3]. Because of the spectral properties of the prosthetic groups, visible , electron paramagnetic resonance [7,8] magnetic circular dichroism [9] and emission [lo] spectroscopy have been used to provide structural and physical information about the enzyme. In addition, resonance Raman (RR) spectroscopy is an invaluable technique for providing detailed insights into the structure and environment of heme in hemoproteins.…”