Distal arginine

Four more amino acid residues are conserved at the distal (arginine and phenylalanine) and proximal (aspartate and phenylalanine) sides of the heme pocket in all structurally characterized ligninolytic peroxidases [33], two of them (distal arginine and proximal aspartate) also being conserved in the other members of the superfamily. 

Redaelli C, Monzani E, Santagostini L et al (2002) Characterization and peroxidase activity of a myoglobin mutant containing a distal arginine. ChemBioChem 3 226-233... 

In both peroxidases, the decay of Compound I is drastically increased by the deletion of the distal arginine, emphasizing its role as a stabilizer of the high-valent intermediate [169-171, 173, 175]. Crystallographic and resonance Raman data have shown that the distal arginine is very flexible, and can move towards or away from the ligand in the sixth position as needed [135, 176]. This flexibility allows the gua-... 

H-bonded to a propionate in ARP, but in LIP Aspl83 H-bonds via its carboxylate side chain. It has been proposed that this carboxylate-carboxylate H-bond may give rise to the low pH optimum found for the reduction of substrates by LIP (Section V,B). Also, the distal Arg43 H-bonds directly with a propionate in LIP, but in ARP and CCP, a water molecule links the distal arginine to both propionate groups via H-bonds. 

The key active-site residues in MPO are shown in Fig. 8. The N3 atom of the proximal His336, which extends from helix H8C, is coordinated to the iron, and the N1 atom forms a H-bond with the side chain of Asn421. In the distal heme pocket, His95 is located 5.7 A from the iron, a separation similar to that found in CCP (5.5 A) (18) and LIP (5.3 A) (5), and Arg239 is also in an equivalent position to the distal arginines in CCP, LIP, and ARP (Figs. 2,4, and 6). Thus, it appears that a number... 

In the extensively studied monoheme yeast CCP (YCCP) and HRPC, the distal cavity of the peroxidatic heme contains conserved arginine and histidine residues, positioned to maximize the rate of heterolytic oxygen cleavage in compound I formation. In both YCCP and HRPC,... 

Figure 6.2 The mechanism of cytochrome-c-peroxidase complex formation, (a) Native enzyme, (b) Activated complex with the acid-base catalytic function of distal histidine (His) and stabilization of negative charge by arginine (Arg) residue of the active site, (c) Hypothetic intermediate oxene complex, (d) Complex I after intramolecular electron regrouping of oxene complex with Fe4+ and free radical X fragment formation.

Fig. 5.4 Schematic representation of the Poulos-Kraut peroxidase mechanism in which the conserved distal histidine serves as an acid-base catalyst that transfers a proton from the H202 to the terminal oxygen after formation of the [Fe(III)-OOH] intermediate. The proximal histidine iron ligand and the catalytic histidine and arginine are shown. In HRP, these residues are His 170,...

Figure 12. Key catalytic residues and the location of L-arginine in the heme active site [100]. The heme is ligated to a cysteine residue with the sixth position vacant. Dashed lines represent hydrogen-bonding interactions between the substrate and the distal heme environment as depicted in Ref.

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