Cytochrome oxidase spectrum

FIGURE 4.2 Linewidth increase with temperature for an S = 1/2 system. The linewidth of a feature in the low-spin heme spectrum from cytochrome a in bovine heart cytochrome oxidase has been fit as a convolution of a constant component from inhomogeneous broadening and a temperature-dependent component from homogeneous broadening (Hagen 2006). (Reproduced by permission of The Royal Society of Chemistry.)... 

Membranes from S. acidocaldarius (DSM 639) contain a malonate-sensitive succinate oxidase that is inhibited by cyanide [30]. The difference spectrum of membranes is indicative of a b-type cytochrome and o- and a-type cytochrome oxidases but provides no indication of a c-type cytochrome. NADH partially reduces the cytochromes when cyanide is present, indicating the presence of a cyanide-resistant pathway [65]. 

There is one report149) that claims that the addition of sulfide to oxidized cytochrome oxidase produces an EPR signal at g of 2.05 and 2.19 due to the previously undetectable Cu(II) (in addition to the normally observed Cu(II) peaks). That occurs immediately upon mixing, before the known reduction of the oxidase by sulfide can occur (1 min or less) and is claimed due to sulfide binding to the heme Fe(lII) which was previously coupled to the Cu(II). That report by Seiter, Angelos and Perreault149) is extremely significant and deserves detailed scrutiny and confirmation. It represents the only occasion of the simultaneous observation of the EPR spectrum of all four metals in the oxidized state. 

The iron in normally oxidized (resting) cytochrome oxidase presents a clear cut low spin Fe(III) EPR spectrum. The peaks found at g = 3.03,2.21,1.45 account for one Fe(III) per oxidase with no indication of interaction with other magnetic cen-ters140 142,143,145). The other iron is EPR inactive in the oxidized state. Treatment by CO, CN-, N3 or F do not affect the low spin signal140) and upon reduction by cytochrome c and other reductants, that signal is the first to respond (by decreasing)142). 

MCD spectra147,148) and their temperature dependence for mixed spin ferric hemes are dominated by the low spin component. The spectrum of oxidized cytochrome oxidase shows a strong temperature dependent peak in the Soret region... 

The resonance Raman spectrum of cytochrome oxidase has also been reported160). 

ORD measurements on alkali-denatured cytochrome oxidase did not show Soret Cotton effects in the oxidized state, but a complex spectrum appeared at pH 11.6 in the reduced state, indicating heme-heme interactions. Polylysine-heme complexes were used as models (252). The optical activity of both oxidized and reduced heme a was measured in various solvents and under different conditions (253, 254). 

Studies on the temperatures dependence of the oxygen reduction rate have revealed that cytochrome oxidase exists in two conformations— hot (h) and cold (c). The respective activation energies and are equal to 16 kJ mol (at 23-35°C) and 60 kJ/mol (below 20°C) [27]. A phase transition accompanied by changes in conformation and the absorption spectrum takes place between 18° and 23°C. The temperature depends on the... 

The chemistry of cytochrome oxidase is not well known. From its spectrum the prosthetic group isolated by Negelein is similar to that of a hemin from the snail, Spirographis. This compound contains the structure l,3,5,8-tetramethyl-2-formyl-4-vinylporphin-6,7-propionic acid. A very similar compound has been crystallized recently from horse heart muscle, but its precise structure is not yet established. A green protein isolated from bile salt-solubilized particles has been... 

Of the a and b cytochromes little is known save that the haem of cyto-chrome-a is similar to that in chlorocruorin and that the haem of cytochrome-6 is protohaem. Cytochrome-a is not autoxidizable (modification, of the valency of the iron by the action of molecular oxygen) whilst cytochrome-6 is. It has been possible to identify three new haemochromogens whose spectra are similar to the spectrum of c3rtochrome -a these are cyto-chromes-fli, -a and -a. C3rtochromes-ai and -a replace cytochrome-a in certain bacteria where this latter substance is missing. Cytochrome-Cs is identical with cytochrome-oxidase, otherwise known as Warburg s respiratory enzyme. In the ferrous state it is autoxidizable, that is, it is oxidized to the ferric state by molecular oxygen. Cytochrome-a, which is not autoxidizable, is oxidized by cytochrome-aj (cytochrome-oxidase). 

Degradation in polypropylene fibers and films is characterized by the following phenomena reduction in mechanical properties, crack formation in the early stage of implantation and decomposition of the implant over a longer period, no changes in molecular mass during implantation, formation of a carbonyl band in the IR spectrum, increase in oxidoreductase and cytochrome-oxidase in the capsule around the implant... 

Figure 1. Difference spectrum (reduced vs oxidized) of beef heart mitochondria. Peak 1 represents cytochrome oxidaser peak 2 cytochrome b, peak 3 cytochromes c and ci. Average concentrations calculated according to Williams . Cytochrome oxidase 26 8 pN, cytochrome b 20.3 pM, cytochrome ci 3.1 pM and cytochrome c 5.1 pM. Protein 13.4 mg ml i. Reductants A. Ascorbate +...

Fig. 19. Absorption spectrum of P. cytochrome oxidase. Approximately 1.3 mg. of the sample at the final stage of purification was dissolved in 1 ml. of 0.1 Af phosphate buffer (pH 6.0). The absorption spectrum was measured at room temperature (22°C.). Solid line, oxidized form broken line, dithionite-reduced form. To obtain the molecular extinction the ordinate was multiplied by 23.5 x 10 (2S0-S00 mi ) or 7.2 X 10 (500-700 m,i).

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