Hemes and hemoproteins

Aron, Janine; Baldwin, David A.; Marques, Helder M.; Pratt, J. M.; Adams, Paul A.

doi:10.1016/0162-0134(86)80064-2

Cited by 158 publications

(128 citation statements)

References 49 publications

Supporting

Mentioning

121

Contrasting

Order By: Relevance

“…Therefore greater 80 electrostatic repulsion can occur and dimerisation is more sensitive to ionic strength. As was reported by Aron et al 64 , a decrease in Soret band absorbance was also observed with increasing ionic strength, particularly at buffer concentrations greater than 0.1 M.Further evidence to support the theory of aggregation at high 85 ionic strength is gained when the effect of ionic strength on  0 is repeated with cyclodextrin-modified NAcMP-11 (CD-NAcMP-11). As with NAcMP-11, a decrease in activity is observed on increasing phosphate concentration up to 0.1 M. Increasing the ionic strength further has little effect on  0 however.…”

supporting

confidence: 59%

“…showed that dimerisation resulted in a decrease in Soret band 60 intensity in aqueous solution 64 . Here, the absorbance at 399 nm for MP-11 was found to increase slightly on alcohol addition, although this in itself is not conclusive evidence that aggregation-dispersion phenomena are responsible for the results observed.…”

Section: Increase In  0 At Low Alcohol Concentrationsmentioning

confidence: 99%

See 1 more Smart Citation

The effect of solvent on the catalytic properties of microperoxidase-11

O’Reilly

Magner

2011

Phys. Chem. Chem. Phys.

View full text Add to dashboard Cite

The effect of a range of solvents on the catalytic oxidation of methyl phenyl sulfide to methyl phenyl sulfoxide by MP-11 and by a cyclodextrin derivative of MP-11 was examined. The addition of low concentrations of alcohols enhanced the initial rate of sulfoxidation rate, most likely due to dispersion of MP-11 aggregates. Higher alcohol concentrations resulted in a decrease in activity arising from solvation of the hydrophobic sulfide, disrupting binding to the catalyst. In alcohols 10 the yield of product was decreased arising from increased rates of MP-11 deactivation via the formation of aldehydes (for primary alcohols) or by peroxide deactivation. The catalytic activity of cyclodextrin modified MP-11 was similar to that of MP-11 itself, demonstrating that it is the Ntermianal side of MP-11 which is the determinant of catalytic activity. Introduction 15The function of enzymes and proteins in non-aqueous solvents has been well established and, in some cases, commercialised [1][2][3][4][5] . Enzyme catalysis and biosensing in organic solvents offers many advantages over aqueous-based processes including increased substrate/analyte solubility, enhanced thermal stability, more 20 favourable reaction thermodynamics, ease of product / biocatalyst recovery and modified selectivity 1,2,[6][7][8][9][10] . The peroxidases are an important group of enzymes which catalyse a wide variety of synthetically useful oxidation reactions using peroxides as oxidants. In spite of this, their potential in non-aqueous catalytic 25 systems has yet to be realised. This may, in part, be attributed to deactivation of the enzymes by the peroxide oxidant at the concentrations required for such reactions [10][11][12] . Strategies to overcome this problem have been developed, including the slow addition 13 or in-situ generation 14 of the peroxide. Alternatively, 30 studies have shown that a high concentration of substrate relative to the peroxide aids the regeneration of the native enzyme and prevents the formation of the peroxidase intermediates which result in enzyme deactivation [15][16][17] . Microperoxidases (MPs) are the products of the proteolytic 35 digestion of cytochrome c. MP-11 contains residues 11 -21 of the parent protein and is prepared by the action of pepsin on cytochrome c. The haem group is covalently attached to the Cys14 and Cys17 residues via sulfide bonds and is coordinated on the proximal side by the imidazole nitrogen of His18. The 6th axial 40 ligand position is either unoccupied or loosely coordinated by water 18 . In this respect the haem configuration is analogous to that of the peroxidase enzymes and MP-11 displays typical peroxidase activity.The array of reactions catalysed by MPs is extensive. The 45 oxidation of phenolic substrates 17,19,20 , peroxide decomposition 21 , sulfide oxidation 22 , Mn 2+ oxidation 23 , the nitration of phenol in the presence of NO 2 -24 , the oxidation of N-methylcarbazole 25 and the dehalogenation of halophenols 26 have all been reported. Thus MPs display activity similar not on...

show abstract

supporting

confidence: 59%

Section: Increase In  0 At Low Alcohol Concentrationsmentioning

confidence: 99%

The effect of solvent on the catalytic properties of microperoxidase-11

O’Reilly

Magner

2011

Phys. Chem. Chem. Phys.

View full text Add to dashboard Cite

show abstract

“…A different approach involves the use of heme-peptide complexes (called microperoxidases) obtained from the proteolysis of horse heart cytochrome c [20,21]. However, while bearing the advantages of good water solubility and reduced tendency to aggregate, which are helpful for the comparison with the proteins, microperoxidases suffer the problem of containing a different type of heme (heme c) in their structure.…”

Section: Introductionmentioning

confidence: 99%

pH-dependent redox and CO binding properties of chelated protoheme-l-histidine and protoheme-glycyl-l-histidine complexes

et al. 2005

View full text Add to dashboard Cite

The pH dependence of redox properties, spectroscopic features and CO binding kinetics for the chelated protohemin-6(7)-L-histidine methyl ester (heme-H) and the chelated protohemin-6(7)-glycyl-L-histidine methyl ester (heme-GH) systems has been investigated between pH 2.0 and 12.0. The two heme systems appear to be modulated by four protonating groups, tentatively identified as coordinated H 2 O, one of heme's propionates, Ne of the coordinating imidazole, and the carboxylate of the histidine residue upon hydrolysis of the methyl ester group (in acid medium). The pK a values are different for the two hemes, thus reflecting structural differences. In particular, the different strain at the Fe-N e bond, related to the different length of the coordinating arm, results in a dramatic alteration of the bond strength, which is much smaller in heme-H than in heme-GH. It leads to a variation in the variation of the pKa for the protonation of the N e of the axial imidazole as well as in the proton-linked behavior of the other protonating groups, envisaging a cross-talk communication mechanism among different groups of the heme, which can be operative and relevant also in the presence of the protein matrix.

show abstract

“…MP8 was prepared by the enzymatic digestion of horse-heart cytochrome c according to the procedure reported in the literature (8), and its concentration was determined by the chromogen method (8). 4-Fluorophenol, 4-chlorophenol, 4-bromophenol, 4-methoxyphenol, and sodium methoxide were purchased from Janssen Chimica (Beerse, Belgium).…”

Section: Methodsmentioning

confidence: 99%

Microperoxidase/H ₂ O ₂ -mediated alkoxylating dehalogenation of halophenol derivatives in alcoholic media

Osman

Boeren

Boersma

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

The results of this study report the H 2 O 2 -driven microperoxidase-8 (MP8)-catalyzed dehalogenation of halophenols such as 4-f luorophenol, 4-chlorophenol, 4-bromophenol, and 2-f luorophenol in alcoholic solvents. In methanol, the conversion of the para-halophenols and 2-f luorophenol to, respectively, 4-methoxyphenol and 2-methoxyphenol, as the major dehalogenated products is observed. In ethanol, 4-ethoxyphenol is the principal dehalogenated product formed from 4-f luorophenol. Two mechanisms are suggested for this MP8-dependent alkoxylating dehalogenation reaction. In one of these mechanisms the oxene resonant form of compound I of MP8 is suggested to react with methanol forming a cofactor-peroxide-alkyl intermediate. This intermediate reacts with the reactive -electrons of the substrate, leading to the formation of the alkoxyphenols and the release of the f luorine substituent as f luoride anion.

show abstract

Hemes and hemoproteins

Cited by 158 publications

References 49 publications

The effect of solvent on the catalytic properties of microperoxidase-11

The effect of solvent on the catalytic properties of microperoxidase-11

pH-dependent redox and CO binding properties of chelated protoheme-l-histidine and protoheme-glycyl-l-histidine complexes

Microperoxidase/H ₂ O ₂ -mediated alkoxylating dehalogenation of halophenol derivatives in alcoholic media

Contact Info

Product

Resources

About

Hemes and hemoproteins

Cited by 158 publications

References 49 publications

The effect of solvent on the catalytic properties of microperoxidase-11

The effect of solvent on the catalytic properties of microperoxidase-11

pH-dependent redox and CO binding properties of chelated protoheme-l-histidine and protoheme-glycyl-l-histidine complexes

Microperoxidase/H 2 O 2 -mediated alkoxylating dehalogenation of halophenol derivatives in alcoholic media

Contact Info

Product

Resources

About

Microperoxidase/H ₂ O ₂ -mediated alkoxylating dehalogenation of halophenol derivatives in alcoholic media