Cytochrome oxidases bacterial

Cytochrome enzymes, 2, 772 Cytochrome a3 oxidase, 6, 697 Cytochrome c oxidase, 6, 683 copper complexes, 2,724,772 Cytochrome oxidases, 6, 624 bacterial, 6,696... 

Figure 14.10 (Left) The CuA site in bacterial cytochrome oxidase. (From Messerschmidt et al., 2001. Reproduced with permission from John Wiley Sons., Inc.) (Right) The haem-a3/CuB site in the resting form of oxidized bovine heart cytochrome c oxidase showing peroxide bound between the haem Fe and CuB. (From Bento et al., 2006. With kind permission of Springer Science and Business Media.)...

Nitrite reductases and nitrous oxide reductases are relatively newly found copper-containing proteins involved in bacterial denitrification. N2O reductase may bear a relationship to cytochrome oxidase and, indeed, parallels it somewhat in function, being the terminal electron acceptor in its pathway. 

Complex IV Cytochrome c to 02 In the final step of the respiratory chain, Complex IV, also called cytochrome oxidase, carries electrons from cytochrome c to molecular oxygen, reducing it to H20. Complex IV is a large enzyme (13 subunits Mr 204,000) of the inner mitochondrial membrane. Bacteria contain a form that is much simpler, with only three or four subunits, but still capable of catalyzing both electron transfer and proton pumping. Comparison of the mitochondrial and bacterial complexes suggests that three subunits are critical to the function (Fig. 19-13). 

Cytochrome oxidase (cytochrome aa3) represents the most important cytochrome of the a class. This is the terminal oxidase used in animals, plants, yeasts, algae and some bacteria. It contains two copper centres, giving four redox groups in total. This oxidase is discussed with other cytochromes that have a terminal oxidase function in Sections 62.1.12.4 and 62.1.12.5. These are cytochromes o, d and cd,. The oxidases fed719 and ax are not included in that discussion. The situation regarding cytochrome ax has been confused, partly due to uncertainty in the definition of this cytochrome. In some respects, the properties of cytochrome ax resemble those of mitochondrial and bacterial aa3. It functions as a terminal oxidase in some bacteria,720 but its role in E. coli is unknown. A soluble fraction from disrupted E. coli cells grown anaerobically on glycerol and fumarate contains a hemoprotein similar to cytochrome ax, which has catalase and peroxidase activity.721... 

Azurin is involved in the electron-transfer chain to cytochrome oxidase in bacterial respiration. Reduction of oxidized azurin by cytochrome c551 is very fast,946 947 but the reverse process is complicated through the existence of a slow conformational equilibrium. 

Bacterial cytochrome oxidases offer an interesting area of study that complements well that of mitochondrial cytochrome oxidase. In some cases they are readily solubilized from the membrane they tend to have fewer subunits than the mitochondrial oxidase and they form stable intermediates during the reaction with dioxygen. They often do not have a role in energy transduction, a fact reflected in their simpler structures. 

Poole1305 has reviewed the bacterial cytochrome oxidases, and has drawn attention to features which are not present in the mitochondrial enzyme, and which reflect the metabolic diversity and adaptability of bacteria. These are (1) the synthesis of the oxidases is controlled dramatically by the prevailing environmental conditions (2) some oxidases are multifunctional, and may use electron acceptors other than dioxygen (3) more than one type of oxidase may be present, each terminating a branched electron-transfer pathway. 

Non-porphyrin FeIV=0 has been detected in bacterial cytochrome oxidases containing a chlorin cytochrome d at a slightly higher frequency (815 cm-1) than that seen in porphyrins [206]. In contrast, the non-haem ferryl model compound analysed by Leising et al. [130] has a significantly lower stretch for the FeIV=0 bond (666 cm-1). 

The interesting issue of proton collection at the protein surface is not addressed here, but it does appear that proton antennae are designed surface features of several proton translocating proteins, including the bacterial RC (Adelroth et al., 2001), cytochrome oxidase (Marantz el at, 1998), and bR (Checover et al., 1997). 

Hosier, J. P., Ferguson-Miller, S., Calhoun, M. W., Thomas, J. W., Hill, J., Lemieux, L., Ma, J., Georgiou, C., Fetter, J., Shapleigh, J., Tecklenburg, M. M. J., Babcock, G. T., and Gennis, R. B., 1993, Insight into the active site structure and function of cytochrome oxidase by analysis of site-directed mutants of bacterial cytochrome aaj and cytochrome bo, J. Bioener. Biomemhr. 25 121nl36. 

The mammalian cytochrome oxidase consists of 13 subunits, of which the three heaviest (subunits I, If, and Iff) are encoded in mitchondrial DNA. The additional 10 smaller subunits are encoded in nuclear DNA, and do not have counterparts in the bacterial enzymes. Their function is stiU mostly enigmatic, but many of them have been... 

However, today a wealth of evidence suggests that cytochrome oxidase functions as a redox-linked proton pump [155] (reviewed in Refs. 8, 14, 47, 52, 92, 99). Two electrical charge equivalents are proposed to cross the membrane per transferred electron two protons are taken up from the M side, one of which is transported to the C side (Fig. 3.6). This function has been confirmed also for cytochrome oxidase liposomes [52,54,55,156-161], and includes work with bacterial cytochrome oxidase... 

Azurin is involved in the electron-transfer chain to cytochrome oxidase in bacterial respiration. 

The bacterial luminescence method, despite its great sensitivity, can be applied accurately only in the oxygen concentration range between 10-6 and 10 8M. Hence, its usefulness is restricted to highly specialized fields like the kinetics of cytochrome oxidase-oxygen reaction (Schindler, 1964 Oshino et al., 1972 Chance et al., 1978 Lloyd et al., 1981). 

Azurin from Pseudomonas aeruginosa has a redox potential of 330 mV [80]. Its physiological function may be single-electron transfer to the cytochrome oxidase of bacterial respiration chains [98-100],... 

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