Tyrosine residues cytochrome

Turnover number, succinate dehydrogenase, 236-237 Tyrosine residues cytochrome hi reductase, 163 cytochrome c peroxidase, 355 glyceraldehyde-3-phosphate dehydrogenase, 21... 

Fe atoms. It had been anticipated that the c-type cytochrome center would have His/Met coordination, but His/His is observed. The former is the more usual coordination, especially at the high potential end E° > +200 mV) ofthe typical bacterial electron transfer chain to which the nitrite reductase is connected (Fig. 2) (7). The second curious feature is that the di heme iron is also six-coordinate thus, the enzyme does not offer a substrate-binding site at either heme. In addition to an expected axial histidine ligand there was an axial tyrosine (residue 25) ligand to the d heme (Fig. 4a). Each monomer is organized into two domains. 

Janing, G. R., Kraft, R., Blanck, J., Rabe, H., and Ruckpaul, K. (1987). Chemical modification of cytochrome P-450 LM4. Identification of functionally linked tyrosine residues. Biochim. Biophys. Acta. 916, 512-523. 

Unfortunately, despite the great stability of the tyrosine radical of ribonucleotide reductase [69], the crystals available for diffraction contain the enzyme in its non-radical form [107]. However, the tyrosine residue (Tyr-122) known to convert to the radical is buried in the protein [99] and the position and structure of the tyrosine residue in the crystal is consistent with spectroscopic data for the radical form as with cytochrome c peroxidase, it appears unlikely that major conformational changes occur subsequent to radical formation. 

The center-to-center distance from either of the BChls of P to the nearest heme in the cytochrome subunit is about 21 A. A tyrosine residue of the protein sits squarely in the path from the heme to P [102]. Because the complete amino acid sequence of the cytochrome subunit has not yet been fitted to the crystallographic map of the reaction center, it is not clear which two of the four hemes are the low-potential hemes, and which two the high-potential, but information on this point should be available shortly. 

Electrons from cytochrome c are donated to the dinuclear copper centre Cua, and then transferred consecutively one at a time to haem a, and from there to the dinuclear haem-copper (haem u -Cua) catalytic centre. A tyrosine residue, Y(I-288), which is covalently cross-linked to one of the Cub ligands (His 240), is also part of the active site. The structure of the four-subunit CcO from R. spheroides is presented in Figure 13.9(a), while a more detailed view of the redox-active cofactors and amino acid residues involved in the proton transfer pathways is given in Figure 13.9(b) (Brzezinski Johansson, 2010). 

Models have been developed to accommodate the results of the hydroxyla-tion of substrates with different structures. The cytochrome P450CAM camphor hydroxylase from the bacterium Pseudomonas putida has been studied by X-ray crystallography. The importance of hydrophilic interactions with a valine (VAL-247) and a polar interaction mediated by hydrogen bonding to a tyrosine residue (TYR-96) has been noted. A model based on the hydroxylation of numerous cyclic amides by Beauveria sulfurescens (originally named Sporotrichum sulfurescens) showed that hydroxylation occurred preferentially at a methylene group about 5.5 A from an electron-rich substituent on the substrate. 

Figure 2. (a) Surface histidine and tyrosine residues and heme of CCP superimposed on the Ca backbone. The cytochrome c binding domain is centered at the arrow, (b) Surface histidine residues and heme of horse heart myo obin. 

Figure 6.8. (A) Structure of cytochrome-c oxidase and (B) synthetic model compound (C) mechanism proposed for O2 reduction hy the fully reduced and mixed valence cytochrome-c oxidase. The rectangle represents the heme-a3/CuB active site YOH is a tyrosine residue F is an intermediate.

Different proteins containing tyrosine residues have been analyzed and linked to the polysaccharides (mainly chitosan) such as gelatin [16], cytochrome c [20],... 

Noronha M, Santos R, Paci E et al (2009) Fluorescence lifetimes of tyrosine residues in cytochrome c" as local probes to study protein unfolding. J Phys Chem B 113 4466-4474... 

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