Cytochrome oxidase, mechanism properties

The most intriguing question regarding molecular mechanism concerns the nature of the molecular linkage between the acidic group and the redox centre. In cytochrome oxidase the formyl carbonyl and the propionate carboxyls of haem a have specific properties that make them potential candidates for providing such a linkage [92,99,167-169]. 

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... 

Abresch et aL, 1998] and of the lumen-side domain of cytochrome/[Martinez et al., 1996]. Finally, in cytochrome c oxidase, two independent theoretical studies have predicted the hydration of buried cavities implicated in the uptake of protons [Riistama et al, 1997 Hofacker and Schulten, 1998]. Although these water molecules were not resolved in published crystallographic structures of the P. denitrificans [Iwata et al, 1995] and bovine heart [Tsukihara et al, 1996] enzymes, many of them are well-defined in a new structure of the Rb, sphaeroides enzyme [M. Svensson-Ek, personal communication]. Understanding the molecular properties giving rise to proton transport in hydrogen-bonded networks containing water molecules is therefore an important step towards the elucidation of proton-pumping mechanisms. 

Since mitochondrial cytochrome c was available commercially (horse heart muscle being the most common source) and could readily be purified to a high level, it formed the basic subject for most of the pioneering studies. Many ideas concerning the electrochemical mechanism, in particular, the mode of interaction with the electrode, have developed around the considerable wealth of information that is available [14, 18] on the structure and properties of the protein molecule. The extent to which the metal centre is buried is illustrated well in Fig. 1 which shows the 3D structure [19] of yeast (iso-1) cytochrome c and a view of the exposed active site. The major function of cytochrome c is as electron donor to cytochrome c oxidase (Complex IV), the membrane-bound enzyme that is the terminus of the aerobic respiratory chain and a site for proton translocation. Another physiological oxidant of cytochrome c (in yeasts) is cytochrome c peroxidase, a soluble enzyme whose crystal structure is known (see Sect. 7). The most important reduc-tant of cytochrome c is the cytochrome Cj component of the membrane-bound hcj complex (Complex III), but others (see Sect. 6, Scheme 5) include cytochrome b, sulfite oxidase, and flavocytochrome (lactate dehydrogenase, found in yeasts). 

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