Magnetization of fast and slow oxidized cytochrome c oxidase

Abstract

Oxidized cytochrome c oxidase can now be prepared either to react rapidly (fast) or to react slowly (slow) with cyanide [Baker, G.M., Noguchi, M., & Palmer, G. (1987) J. Biol. Chem. 262, 595-604]. Slow oxidized cytochrome c oxidase is also characterized by an integer spin g = 12 EPR signal which is absent in the fast form. The saturation magnetization of two samples of both forms of cytochrome oxidase has been studied at four applied magnetic fields (0.3125, 1.25, 2.5, and 5.0 T) over a temperature range from 2 to 200 K using a superconducting susceptometer. The saturation magnetization data of the two preparations are readily distinguished. The data for the coupled cytochrome a3: CuB site of both preparations are most simply interpreted as exhibiting S = 2 paramagnetism with D = +13 cm-1 for the fast and D = -7 cm-1 for the slow forms, respectively. However, there is some indication that the fast form is a mixture of both S = 2 and S = 1 paramagnetic species while the slow form is only S = 2.

Copper Active Sites in Biology

“…This issue has not been resolved, but we note that in resting CcO, the heme a 3 is high-spin (S = 5/2) based on 1) the λ max of the heme Soret band in the absorption spectrum of resting CcO that appears at 424 nm, indicative of a high-spin electronic structure, 1077,1078 2) SQUID magnetization studies that have demonstrated that the heme a 3 —Cu B pair is antiferromagnetically coupled to yield an overall S = 2 spin system, 1079,1080 and 3) EPR and MCD on resting ubiquinol oxidase that further indicates a small, anisotropic superexchange parameter ( J ≈ 1 cm −1 ) and a large positive zero-field splitting ( D = 5 cm −1 ) for heme a 3 . 1081 These spectroscopic observations are contradictory to those for the heme-peroxo-copper model complex, wherein the analogous end-on bridging peroxide causes the heme to be LS.…”

The site of the redox‐linked proton pump in eukaryotic cytochrome c oxidases

“…While this site is undoubtedly involved in consumption of the 'scalar' protons required for generation of the product water, it is extremely difficult to envisage it simultaneously involved in 'vectorial' proton translocation by a ligand exchange mechanism. However, in the case of derivatives like the fully oxidized resting and pulsed enzyme where heme a3 is magnetically coupled to CuB [29], presumably through bridging ligands, it is conceivable that ligand exchange processes at CuB might manifest themselves as perturbations in the spectral characteristics of heme as. Thus, by a process of elimination, the present data suggest CUB to be the site of the proton pump.…”

One Heme, Diverse Functions: Using Biosynthetic Myoglobin Models to Gain Insights into Heme‐Copper Oxidases and Nitric Oxide Reductases

“…Numerous spectroscopic studies have shown that the heme-copper site in HCO is spin-coupled in its Fe III -Cu B II resting state, suggesting that a ligand bridges the heme iron and copper 31,84–87. The X-ray crystals of HCO from Paracoccus denitrificans 15 and bovine heart37 show electron density between the two metal centers, providing evidence to support a bridging ligand.…”