"Peroxidatic" form of cytochrome oxidase as studied by X-ray absorption spectroscopy

Abstract

X-ray absorption spectroscopy shows pulsed oxidase to be similar to resting oxidase but to lack the sulfur bridge between iron and copper of active sites (Powers, L., Y. Ching, B. Chance, and B. Muhoberac, 1982, Biophys. J., 37[2, Pt. 2]: 403a. [Abstr.] ) The first shell ligands and bond lengths of the pulsed oxidase active site heme most clearly fit the ferric peroxidases from horseradish and yeast, and the pulsed oxidase cyanide compound resembles the low spin hemoprotein cyanide compounds. The structural results are consistent with an aquo or a peroxo form for pulsed oxidase as is also observed by optical studies. These structural and chemical data are consistent with a role for the pulsed forms in a cyclic peroxidatic side reaction in which the pulsed and pulsed peroxide compounds act as peroxide scavengers. The peroxidatic role of cytochrome oxidase in the nonsulfur bridged form suggests the renaming of the "oxygenated" or "pulsed" forms on a functional basis as "peroxidatic" forms of cytochrome oxidase.

Cytochrome c oxidase from Paracoccus denitrificans: both hemes are located in subunit I.

“…These coefficients are slightly different from the classical values reported for the bovine enzyme by Vanneste (28). Since CUB is strongly associated with cytochrome a3 (29) and since its spectral properties are not modified, it can be concluded that CUB is also present in the one-subunit enzyme.…”

“…Since this center is detected spectroscopically and by electron paramagnetic resonance (12,29), it should be possible to confirm this hypothesis by using our one-subunit preparation.…”

Chemiosmotic coupling in cytochrome oxidase

“…1,Cl that i and o redox centres may be situated on either side of CUB is consistent with the conclusion, drawn from optical absorption, EPR and MCD studies, that ligands, such as NO and CN- [18], or NO and NT [19,20], or CO and Hz0 [21] may be simultaneously bound at separate centres neighbouring CUB, and that electrons may be conducted between these centres, presumably via CUB ( [21,22] and see [23,24]). It is also consistent with the inference that, on photolysis of the CO compound of the oxidase, the CO migrates from a site between a3 and CUB to a pocket neighbouring CUB [25-271. It is a fundamental, and potentially diagnostic, attribute of the protonmotive 0 loop flow system ( fig.…”

X‐ray absorption studies on bacteriorhodopsin

“…The EXAFS data for the Fe-bR samples were collected at the Stanford Synchroton Radiation Laboratory (SSRL) on beamline II-2 as described [14][15][16]. All samples were kept at -100°C during data collection.…”