Cyanide peroxidase

In the case of His/CN systems, structurally pertinent to myoglobin cyanide, peroxidase cyanide, cytochrome c cyanide and the CN derivative of a cytochrome c mutant, where the axial ligand methionine is substituted with alanine (Ala80-cyt c-CN), the simple assignment of the four methyl protons, which is an almost trivial task nowadays, provides direct structural information on the axial ligands, which can be used for structural analysis in solution. The chemical shifts for each... 

Covalent ferric compounds Bright red Two diffuse bands in the green Azide MetHb 575, 542 HS. MetHb 570, 545 Cyanide peroxidase 581.5, 542... 

Thiocyanate ion, SCN , inhibits formation of thyroid hormones by inhibiting the iodination of tyrosine residues in thyroglobufin by thyroid peroxidase. This ion is also responsible for the goitrogenic effect of cassava (manioc, tapioca). Cyanide, CN , is liberated by hydrolysis from the cyanogenic glucoside finamarin it contains, which in turn is biodetoxified to SCN. 

Taurog et al. [216] showed that contrary to previous suggestions, both iodination and coupling are catalyzed by the oxoferryl porphyrin Tr-cation radical of TPO Compound I and not the oxoferryl protein radical. HRP catalyzed the oxidation of bisulfite to sulfate with the intermediate formation of sulfur trioxide radical anion S03 [217] HPO, MPO, LPO, chloroperoxidase, NADH peroxidase, and methemoglobin oxidized cyanide to cyanyl radical [218],... 

In addition to binding to cytochrome c oxidase, cyanide inhibits catalase, peroxidase, methemoglobin, hydroxocobalamin, phosphatase, tyrosinase, ascorbic acid oxidase, xanthine oxidase, and succinic dehydrogenase activities. These reactions may make contributions to the signs of cyanide toxicity (Ardelt et al. 1989 Rieders 1971). Signs of cyanide intoxication include an initial hyperpnea followed by dyspnea and then convulsions (Rieders 1971 Way 1984). These effects are due to initial stimulation of carotid and aortic bodies and effects on the central nervous system. Death is caused by respiratory collapse resulting from central nervous system toxicity. 

Fig. 6. Mechanisms for the reduction of compounds I and II of HRP C by ferulic acid, after Henriksen et al. 195). This scheme is based on new information from the 1.45 A resolution crystal structure of the ternary complex of ferulic acid and cyanide-ligated HRP C 195). The direction of proton transfer is indicated by the dotted arrows. The mechanism is discussed in Section IV,B,2, and the crystal structure data in Section IV,F,4. Note that a distal site water molecule makes an important hydrogen bond with the backbone carbonyl group of Prol39 (a residue conserved in all members of the plant peroxidase superfamily).

The crystal structures of two ferulic acid complexes of HRP C have been solved, one with resting state enzyme (to 2.0 A resolution) and the other with the cyanide-ligated enzyme (to 1.45 A resolution) 195). These represent a major achievement for the crystallography of peroxidase complexes. The binary complex is heterogenous, according to the 2Fo-Fc omit difference electron density map of the active site. The disordered density observed has been interpreted in terms of three... 

Thiosulfate cyanide sulfurtransferase symmetry in 78 TTiiouridine 234 Three-dimensional structures of aconitase 689 adenylate kinase 655 aldehyde oxido-reductase 891 D-amino acid oxidase 791 a-amylase, pancreatic 607 aspartate aminotransferase 57,135 catalytic intermediates 752 aspartate carbamyltransferase 348 aspartate chemoreceptor 562 bacteriophage P22 66 cadherin 408 calmodulin 317 carbonic acid anhydrase I 679 carboxypeptidase A 64 catalase 853 cholera toxin 333, 546 chymotrypsin 611 citrate synthase 702, 703 cutinase 134 cyclosporin 488 cytochrome c 847 cytochrome c peroxidase 849 dihydrofolate reductase 807 DNA 214, 223,228,229, 241 DNA complex... 

Peroxidase is inactivated by anions and certain antimicrobial agents, including azide, cyanide, and thiomersal. Antimicrobial agents may be present in concentrated enzyme label solutions and assay buffers at typically active concentrations, but must not be present in wash solutions or substrate. The latter reagents must be freshly made each day from concentrated stocks. 

Besides using the bioactive agent to detect the ion of interest, another approach can include monitoring an ion by its inhibitory effect upon enzymatic activity. For example, horseradish peroxidase (HRP) can be immobilised onto one gate of a REFET [107] allowing the presence of cyanide ion to be measured at concentrations of 10 3-10 7 M. The approach used here is to monitor the inhibition of the enzymatic HRP effect, by the cyanide ion, on ascorbic acid. Even lower levels (10 10 M) of detection can be obtained using a polyphenol oxidase/clay composite immobilised on carbon, with no interference from chloride, nitrate or bromide [108]. 

Battistuzzi G, Bellei M, De Rienzo F et al (2006) Redox properties of the Fe3+/Fe2+ couple in Arthromyces ramosus class II peroxidase and its cyanide adduct. J Biol Inorg Chem 11 586-592... 

Special conditions the above method is valid for a pure enzyme preparation, but cannot give entirely reliable measurements for impure samples. Interfering reactants in the medium may be allowed for by carrying out recovery experiments with a range of amounts of pure SOD added to the test enzyme preparation. Dialysis of the enzyme preparation will eliminate small molecules that may interfere, like ascorbate, reduced glutathione and catecholamines. The addition of 2 //M cyanide may be used to block peroxidases, which has only a minimal effect on the activity of Cu/Zn-SOD. Alternatively 10-5 M azide may be used to block peroxidases without effect on Cu/Zn-SOD. 

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