Cytochrome active-site structure

Gartner, C. A. (2003) Photoaffinity ligands in the study of cytochrome p450 active site structure. Curr. Med. Chem. 10, 671-689. 

Dawson, J. H. and Sono, M. (1987) Cytochrome P450 chloroperoxidase thiolate-ligand heme enzymes. Spectroscopic determination of their active site structure and mechanistic implication of thiolate ligation. Chem. Rev. 87, 1255-1276. 

The active site structure of peroxidases (Fig. 16-13) is quite highly conserved. As in myoglobin, an imidazole group is the proximal heme ligand, but it is usually hydrogen bonded to an aspartate carboxylate as a catalytic diad (Fig. 16-13).223 In cytochrome c peroxidase... 

Figure 1. Active site structures of (a) cytochrome P450cam (PDB 2CPP), (b) beef liver catalase (PDB 4BLC), and (c) horseradish peroxidase (HRP) (PDB 1ATJ).

Dawson JF1, Sono M (1987) Cytochrome P-450 and chloroperoxidase - thiolate-ligated heme enzymes - spectroscopic determination of their active-site structures and mechanistic implications of thiolate ligation. Chem Rev 87 1255-1276... 

Several enzymes with peroxidase-like action have also been used in immunoassays. Microperoxidases are catalytically active fragments obtained from cytochrome c by proteolytic action. They consist of the heme group covalently coupled to a short peptide alpha helix (26). The active site structure is similar to that of peroxidase Four of the six possible coordination bonds of the iron atom are occupied by bonding to the porphyrin while the fifth complexes with a histidine residue and the sixth is exposed to the environment and forms the catalytically active portion of the molecule. The reaction mechanism and spectrum of substrates is similar to HRP, although the specific activity is variable... 

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. 

Koymans L, Donne-op den Kelder GM, Koppele Te JM, Vermeulen NP. Cytochromes P450 Their active-site structure and mechanism of oxidation. Drug Metab Rev 1993 25 325-87. 

Friedrich, M.G., Giess, F., Naumann, R., Knoll, W., Ataka, K., Heberle, J., Hrabakova, J., Murgida, D.H., and Hildebrandt, P. (2004) Active site structure and redox processes of cytochrome c oxidase immobilised in a novel biomimetic lipid membrane on an electrode. Chemical Communications,... 

Fig. 2. Active-site structure of yeast cytochrome c peroxidase. The dashed lines represent H-bonds between N1 of the distal His52 and the side-chain carbonyl of Asn82, and N1 of the proximal Hisl75 and the side-chain carboxylate of Asp235. This diagram was generated using the X-ray coordinates for the 1.7-A structure of CCP (18).

The sulfite oxidase enzymes are widespread in Nature, and are found in plants, bacteria (the sulfite dehydrogenases) and in birds and mammals. In addition, this family also includes the assimilatory plant nitrate reductases, which have essentially similar molybdenum coordination and differ structurally in lacking an active site arginine that is present in sulfite oxidase, and in showing somewhat different active site structures on turnover. We will focus here on the animal sulfite oxidase enzymes, of which chicken and human are the best studied. In animals the enzyme is responsible for the physiologically essential oxidation of sulfite to sulfate. It is a dimer of 52 kDa subunits and resides in the mitochondrial inner-membrane space. Each monomer contains Mo associated with one molybdopterin, plus a cytochrome heme. The enzymes catalyze the following reaction, which occurs at the Mo site which is reduced from Mo(vi) to Mo(iv) in the process ... 

Given the impressively demonstrated utility of the RR technique as an exquisite probe of the active site structures of these cytochrome P450 species, it is anticipated that it will play a major role in defining the structure of subsequent intermediates in the enzymatic cycle of this class of proteins. However, for such expectations to be realized, it will be necessary to devise effective strategies to trap these highly reactive species, or to prolong their lifetime to an extent sufficient to permit acquisition of their RR spectra. 

McLean KJ, Carroll P, Lewis DG, DunfordAJ, Seward HE, Neeli R, Cheesman MR, Marsollier L, Douglas P, Smith WE, Rosenkrands I, Cole ST, Leys D, Parish T, Munro AW (2008) Characterization of active site structure in CYP121. A cytochrome P450 essential for viability of Mycobacterium tuberculosis H37Rv. J Biol Chem 283 33406-33416... 

Figure 3. Active site structure of cytochrome P-450cam [37,38].

Ekins S, De Groot MJ, Jones JP. Pharmacophore and three-dimensional quantitative structure activity relationship methods for modeling cytochrome P450 active sites. Drug Metab Dispos 2001 29 936-44. 

Ribbon structures of two redox proteins, cytochrome c (a) and plastocyanin (b). The blowups show the active sites where transition metal atoms are located. 

Loew GH, Harris DL. 2000. Role of the heme active site and protein environment in structure, spectra and function of the cytochrome P450s. Chem Rev 100 407. 

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