Biomedical subjects

M H Gold

Publications and source records attributed to M H Gold.

At least 91 records · Page 5Linked to original sources

PubMed1992

Degradation of azo dyes by the lignin-degrading fungus Phanerochaete chrysosporium.

Under nitrogen-limiting, secondary metabolic conditions, the white rot basidiomycete Phanerochaete chrysosporium extensively mineralized the specifically 14C-ring-labeled azo dyes 4-phenylazophenol, 4-phenylazo-2-methoxyphenol, Disperse Yellow 3 [2-(4'-acetamidophenylazo)-4-methylphenol], 4-phenylazoaniline, N,N-dimethyl-4-phenylazoaniline, Disperse Orange 3 [4-(4'-nitrophenylazo)-aniline], and Solvent Yellow 14 (1-phenylazo-2-naphthol). Twelve days after addition to cultures, the dyes had been mineralized 23.1 to 48.1%. Aromatic rings with substituents such as hydroxyl, amino, acetamido, or nitro functions were mineralized to a greater extent than unsubstituted rings. Most of the dyes were degraded extensively only under nitrogen-limiting, ligninolytic conditions. However, 4-phenylazo-[U-14C]phenol and 4-phenylazo-[U-14C]2-methoxyphenol were mineralized to a lesser extent under nitrogen-sufficient, nonligninolytic conditions as well. These results suggest that P. chrysosporium has potential applications for the cleanup of textile mill effluents and for the bioremediation of dye-contaminated soil.

Azo Compounds↗

PubMed1992

Degradation of 2,7-dichlorodibenzo-p-dioxin by the lignin-degrading basidiomycete Phanerochaete chrysosporium.

Under secondary metabolic conditions, the white-rot basidiomycete Phanerochaete chrysosporium degraded 2,7-dichlorodibenzo-p-dioxin (I). The pathway for the degradation of I was elucidated by the characterization of fungal metabolites and oxidation products generated by lignin peroxidase (LiP), manganese peroxidase (MnP), and crude intracellular cell-free extracts. The multistep pathway involves the degradation of I and subsequent intermediates by oxidation, reduction, and methylation reactions to yield the key intermediate 1,2,4-trihydroxybenzene (III). In the first step, the oxidative cleavage of the dioxin ring of I, catalyzed by LiP, generates 4-chloro-1,2-benzoquinone (V), 2-hydroxy-1,4-benzoquinone (VIII), and chloride. The intermediate V is then reduced to 1-chloro-3,4-dihydroxybenzene (II), and the latter is methylated to form 1-chloro-3,4-dimethoxybenzene (VI). VI in turn is oxidized by LiP to generate chloride and 2-methoxy-1,4-benzoquinone (VII), which is reduced to 2-methoxy-1,4-dihydroxybenzene (IV). IV is oxidized by either LiP or MnP to generate 4-hydroxy-1,2-benzoquinone, which is reduced to 1,2,4-trihydroxybenzene (III). The other aromatic product generated by the initial LiP-catalyzed cleavage of I is 2-hydroxy-1,4-benzoquinone (VIII). This intermediate is also generated during the LiP- or MnP-catalyzed oxidation of the intermediate chlorocatechol (II). VIII is also reduced to 1,2,4-trihydroxybenzene (III). The key intermediate III is ring cleaved by intracellular cell extracts to produce, after reduction, beta-ketoadipic acid. In this pathway, initial oxidative cleavage of both C-O-C bonds in I by LiP generates two quinone products, 4-chloro-1,2-benzoquinone (V) and 2-hydroxy-1,4-benzoquinone (VIII). The former is recycled by reduction and methylation reactions to generate an intermediate which is also a substrate for peroxidase-catalyzed oxidation, leading to the removal of a second chlorine atom. This unique pathway results in the removal of both aromatic chlorines before aromatic ring cleavage takes place.

Basidiomycota↗

PubMed1991

Reactions of lignin peroxidase compounds I and II with veratryl alcohol. Transient-state kinetic characterization.

Stopped-flow techniques were utilized to investigate the kinetics of the reaction of lignin peroxidase compounds I and II (LiPI and LiPII) with veratryl alcohol (VA). All rate data were collected from single turnover experiments under pseudo first-order conditions. The reaction of LiPI with VA strictly obeys second-order kinetics over the pH range 2.72-5.25 as demonstrated by linear plots of the pseudo first-order rate constants versus concentrations of VA. The second-order rate constants are strongly dependent on pH and range from 2.62 x 10(6) M-1 s-1 (pH 2.72) to 1.45 x 10(4) M-1 s-1 (pH 5.25). The reaction of LiPII and VA exhibits saturation behavior when the observed pseudo first-order rate constants are plotted against VA concentrations. The saturation phenomenon is quantitatively explained by the formation of a 1:1 LiPII-substrate complex. Results of kinetic and rapid scan spectral analyses exclude the formation of a LiPII-VA cation radical complex. The first-order dissociation rate constant and the equilibrium dissociation constant for the LiPII reaction are also pH dependent. Binding of VA to LiPII is controlled by a heme-linked ionizable group of pKa approximately 4.2. The pH profiles of the second-order rate constants for the LiPI reaction and of the first-order dissociation constants for the LiPII reaction both demonstrate two pKa values at approximately 3.0 and approximately 4.2. Protonated oxidized enzyme intermediates are most active, suggesting that only electron transfer, not proton uptake from the reducing substrate, occurs at the enzyme active site. These results are consistent with the one-electron oxidation of VA to an aryl cation radical by LiPI and LiPII.

Basidiomycota↗

PubMed1991

Lignin peroxidase from the basidiomycete Phanerochaete chrysosporium is synthesized as a preproenzyme.

The cDNA clone L18 encoding lignin peroxidase LiP2, the most highly expressed LiP isozyme from Phanerochaete chrysosporium strain OGC101, was isolated and sequenced. Comparison of the cDNA sequence with the N-terminal sequence of the mature LiP2 protein isolated from culture medium suggests that the mature protein contains 343 amino acids (aa) and is preceded by a 28-aa leader sequence. In vitro transcription followed by in vitro translation and processing by signal peptidase resulted in cleavage at a site following the Ala21 (counted from the N-terminal Met1 of the initial translation product). The resultant protein contains a 7-aa propeptide, indicating that LiP is synthesized as a preproenzyme.

Amino Acid Sequence↗

PubMed1991

NMR study of the active site of resting state and cyanide-inhibited lignin peroxidase from Phanerochaete chrysosporium. Comparison with horseradish peroxidase.

One- and two-dimensional 1H NMR spectroscopy has been used to probe the active site of the high spin ferric resting state and the low spin, cyanide-inhibited derivative of isozyme H2 of the lignin peroxidase, LiP, from Phanerochaete chrysosporium strain BKM 1767. One-dimensional NMR revealed a resting state LiP that is five coordinate at 25 degrees C with an electronic structure similar to that of horseradish peroxidase, HRP. Differential paramagnetic relaxivity was used to identify the C beta H signals of the axial His177. A combination of bond correlation spectroscopy and nuclear Overhauser effect spectroscopy of cyanide-inhibited LiP (LiP-CN) has allowed the assignment of all resolved heme resonances without recourse to isotope labeling, as well as those of the proximal His177 and the distal His48. The surprising effectiveness of the two dimensional NMR methods on such a large and paramagnetic protein indicates that such two dimensional experiments can be expected to have major impact on solution structure determination of diverse classes of heme peroxidases. The two dimensional NMR data of LiP-CN reveal a heme contact shift pattern that reflects a close similarity to that of HRP-CN, including the unusual in-plane trans and cis orientation of the 2- and 4-vinyls. The axial His177 also exhibits the same orientation relative to the heme as in HRP-CN. The proximal His177 contact shifted resonances of both the low spin LiP-CN and high spin LiP are shown to reflect significantly reduced hydrogen bond donation by, or imidazolate character for, the axial histidine in LiP relative to HRP, which may explain the higher redox potential of LiP. The signals are identified for a distal residue that originates from the protonated His48 with disposition relative to the heme similar to that found for the distal His42 in HRP-CN. In contrast, the absence of any resolved signals attributable to an Arg44 in LiP-CN suggest that this distal residue has an altered orientation relative to the heme compared with that of the conserved Arg38 in HRP-CN (Thanabal, V., de Ropp, J. S., and La Mar, G. N. (1987) J. Am. Chem. Soc. 109, 7516-7525).

Basidiomycota↗

PubMed1991

The catalytic site of manganese peroxidase. Regiospecific addition of sodium azide and alkylhydrazines to the heme group.

Manganese peroxidase (MnP), which normally oxidizes Mn2+ to Mn3+, is rapidly and completely inactivated in an H2O2-dependent reaction by 2 equivalents of sodium azide. The inactivation is paralleled by formation of the azidyl radical and high yield conversion of the prosthetic heme into a meso-azido adduct. The meso-azido enzyme is oxidized by H2O2 to a Compound II-like species with the Soret band red-shifted 2 nm relative to that of native Compound II. The time-dependent decrease in this Compound II-like spectrum (t1/2 = 2.3 h) indicates that the delta-meso azido heme is more rapidly degraded by H2O2 than the prosthetic heme of control enzyme (t1/2 = 4.8 h). MnP is also inactivated by phenyl-, methyl-, and ethylhydrazine. The phenylhydrazine reaction is too rapid for kinetic analysis, but KI = 402 microM and kinact = 0.22/min for the slower inactivation by methylhydrazine. Reaction with phenylhydrazine at pH 4.5 does not yield iron-phenyl, N-phenyl, or meso-phenyl heme adducts. Ethylhydrazine inactivates the enzyme both at pH 4.5 and 7.0, but only detectably produces delta-meso-ethyl-heme at pH 7.0. Reconstitution of apo-MnP with hemin or delta-meso-ethylheme yields enzyme with, respectively, 50 and 5% of the native activity. The delta-meso-alkyl group thus suppresses most of the catalytic activity of the enzyme even though a Compound II-like species is still formed with H2O2. Finally, Co2+ inhibits the enzyme competitively with respect to Mn2+ but does not inhibit its inactivation by azide or the alkylhydrazines. The results argue that substrates interact with the heme edge in the vicinity of the delta-meso-carbon. They also suggest that Mn2+ and Co2+ bind to a common site close to the delta-meso-carbon without blocking the approach of small molecules to the heme edge. An active site model is proposed that accommodates these results.

Azides↗

PubMed1991

In vitro depolymerization of lignin by manganese peroxidase of Phanerochaete chrysosporium.

Homogeneous manganese peroxidase catalyzed the in vitro partial depolymerization of four different 14C-labeled synthetic lignin preparations. Gel permeation profiles demonstrated significant depolymerization of 14C-sidechain-labeled syringyl lignin, a 14C-sidechain-labeled syringyl-guaiacyl copolymer (angiosperm lignin), and depolymerization of 14C-sidechain- and 14C-ring-labeled guaiacyl lignins (gymnosperm lignin). 3,5-Dimethoxy-1,4-benzo-quinone, 3,5-dimethoxy-1,4-hydroquinone, and syringylaldehyde were identified as degradation products of the syringyl and syringyl-guaiacyl lignins. These results suggest that manganese peroxidase plays a significant role in the depolymerization of lignin by Phanerochaete chrysosporium.

Basidiomycota↗

PubMed1991

Manganese regulation of manganese peroxidase expression and lignin degradation by the white rot fungus Dichomitus squalens.

Extracellular manganese peroxidase and laccase activities were detected in cultures of Dichomitus squalens (Polyporus anceps) under conditions favoring lignin degradation. In contrast, neither extracellular lignin peroxidase nor aryl alcohol oxidase activity was detected in cultures grown under a wide variety of conditions. The mineralization of 14C-ring-, -side chain-, and -methoxy-labeled synthetic guaiacyl lignins by D. squalens and the expression of extracellular manganese peroxidase were dependent on the presence of Mn(II), suggesting that manganese peroxidase is an important component of this organism's lignin degradation system. The expression of laccase activity was independent of manganese. In contrast to previous findings with Phanerochaete chrysosporium, lignin degradation by D. squalens proceeded in the cultures containing excess carbon and nitrogen.

Kinetics↗

PubMed1991

Degradation of 2,4-dichlorophenol by the lignin-degrading fungus Phanerochaete chrysosporium.

Under secondary metabolic conditions the white rot basidiomycete Phanerochaete chrysosporium mineralizes 2,4-dichlorophenol (I). The pathway for the degradation of 2,4-dichlorophenol (I) was elucidated by the characterization of fungal metabolites and of oxidation products generated by purified lignin peroxidase and manganese peroxidase. The multistep pathway involves the oxidative dechlorination of 2,4-dichlorophenol (I) to yield 1,2,4,5-tetrahydroxybenzene (VIII). The intermediate 1,2,4,5-tetrahydroxybenzene (VIII) is ring cleaved to produce, after subsequent oxidation, malonic acid. In the first step of the pathway, 2,4-dichlorophenol (I) is oxidized to 2-chloro-1,4-benzoquinone (II) by either manganese peroxidase or lignin peroxidase. 2-Chloro-1,4-benzoquinone (II) is then reduced to 2-chloro-1,4-hydroquinone (III), and the latter is methylated to form the lignin peroxidase substrate 2-chloro-1,4-dimethoxybenzene (IV). 2-Chloro-1,4-dimethoxybenzene (IV) is oxidized by lignin peroxidase to generate 2,5-dimethoxy-1,4-benzoquinone (V), which is reduced to 2,5-dimethoxy-1,4-hydroquinone (VI). 2,5-Dimethoxy-1,4-hydroquinone (VI) is oxidized by either peroxidase to generate 2,5-dihydroxy-1,4-benzoquinone (VII) which is reduced to form the tetrahydroxy intermediate 1,2,4,5-tetrahydroxybenzene (VIII). In this pathway, the substrate is oxidatively dechlorinated by lignin peroxidase or manganese peroxidase in a reaction which produces a p-quinone. The p-quinone intermediate is then recycled by reduction and methylation reactions to regenerate an intermediate which is again a substrate for peroxidase-catalyzed oxidative dechlorination. This unique pathway apparently results in the removal of both chlorine atoms before ring cleavage occurs.

Basidiomycota↗

PubMed1991

Manganese peroxidase gene transcription in Phanerochaete chrysosporium: activation by manganese.

The expression of manganese peroxidase in nitrogen-limited cultures of Phanerochaete chrysosporium is dependent on Mn, and initial work suggested that Mn regulates transcription of the mnp gene. In this study, using Northern (RNA) blot analysis of kinetic, dose-response, and inhibitor experiments, we demonstrate unequivocally that Mn regulates mnp gene transcription. The amount of mnp mRNA in cells of 4-day-old nitrogen-limited cultures is a direct function of the concentration of Mn in the culture medium up to a maximum of 180 microM. Addition of Mn to nitrogen-limited Mn-deficient secondary metabolic (4-, 5-, and 6-day-old) cultures results in the appearance of mnp mRNA within 40 min. The appearance of this message is completely inhibited by the RNA synthesis inhibitor dactinomycin but not by the protein synthesis inhibitor cycloheximide. Furthermore, the amount of mnp mRNA produced is a direct function of the concentration of added Mn. In contrast, addition of Mn to low-nitrogen Mn-deficient 2- or 3-day-old cultures does not result in the appearance of mnp mRNA. Manganese peroxidase protein is detected by specific immunoprecipitation of the in vitro translation products of poly(A) RNA isolated from Mn-supplemented (but not from Mn-deficient) cells. All of these results demonstrate that Mn, the substrate for the enzyme, regulates mnp gene transcription via a growth-stage-specific and concentration-dependent mechanism.

Base Sequence↗

PubMed1990

Resonance Raman spectroscopic characterization of compound III of lignin peroxidase.

Resonance Raman (RR) spectra of several compounds III of lignin peroxidase (LiP) have been measured at 90 K with Soret and visible excitation wavelengths. The samples include LiPIIIa (or oxyLiP) prepared by oxygenation of the ferrous enzyme, LiPIIIb generated by reaction of the native ferric enzyme with superoxide, LiPIIIc prepared from native LiP plus H2O2 followed by removal of excess peroxide with catalase, and LiPIII* made by addition of excess H2O2 to the native enzyme. The RR spectra of these four products appear to be similar and, thus, indicate that the environments of these hexacoordinate, low-spin ferriheme species must also be very similar. Nonetheless, the Soret absorption band of LiPIII* is red-shifted by 5 nm from the 414-nm maximum common to LiPIIIa, -b, and -c [Wariishi, H., & Gold, M.H. (1990) J. Biol. Chem. 265, 2070-2077]. Analysis of the iron-porphyrin vibrational frequencies indicates that the electronic structures for the various compounds III are consistent with an FeIIIO2.-formulation. The spectral changes observed between the oxygenated complex and the ferrous heme of lignin peroxidase are similar to those between oxymyoglobin and deoxymyoglobin. The contraction in the core sizes in compound III relative to the native peroxidase is analyzed and compared with that of other heme systems. EPR spectra confirm that the high-spin ferric form of the native enzyme, with an apparent g = 5.83, is converted into the EPR-silent LiPIII* upon addition of excess H2O2. Its magnetic behavior may be explained by anti-ferromagnetic coupling between the low-spin FeIII and the superoxide ligand.(ABSTRACT TRUNCATED AT 250 WORDS)

Basidiomycota↗

PubMed1990

Oxidation of monomethoxylated aromatic compounds by lignin peroxidase: role of veratryl alcohol in lignin biodegradation.

Lignin peroxidase (LiP), an extracellular heme enzyme from the lignin-degrading fungus Phanerochaete chrysosporium, catalyzes the H2O2-dependent oxidation of a variety of nonphenolic lignin model compounds. The oxidation of monomethoxylated lignin model compounds, such as anisyl alcohol (AA), and the role of veratryl alcohol (VA) in LiP reactions were studied. AA oxidation reached a maximum at relatively low H2O2 concentrations, beyond which the extent of the reactions decreased. The presence of VA did not affect AA oxidation at low molar ratios of H2O2 to enzyme; however, at ratios above 100, the presence of VA abolished the decrease in AA oxidation. Addition of stoichiometric amounts of AA to LiP compound II (LiPII) resulted in its reduction to the native enzyme at rates that were significantly faster than the spontaneous rate of reduction, indicating that AA and other monomethoxylated aromatics are directly oxidized by LiP, albeit slowly. Under steady-state conditions in the presence of excess H2O2 and VA, a visible spectrum for LiPII was obtained. In contrast, under steady-state conditions in the presence of AA a visible spectrum was obtained for LiPIII*, a noncovalent complex of LiPIII and H2O2. AA competitively inhibited the oxidation of VA by LiP; the Ki for AA inhibition was 32 microM. Addition of VA to LiPIII* resulted in its conversion to the native enzyme. In contrast, AA did not convert LiPIII* to the native enzyme; instead, LiPIII* was bleached in the presence of AA. Thus, AA does not protect LiP from inactivation by H2O2.(ABSTRACT TRUNCATED AT 250 WORDS)

Anisoles↗

PubMed1990

Characterization of a gene encoding a manganese peroxidase from Phanerochaete chrysosporium.

The complete nucleotide (nt) sequence of a gene (mnp-1) encoding manganese peroxidase isozyme 1 (MnP-1) (pI = 4.9) from Phanerochaete chrysosporium has been determined. The sequence of 2539 bp includes 526 bp of 5'-flanking sequence and 368 bp 3' to the poly(A) site. Comparison of cDNA and genomic sequences indicates six introns varying in size from 57-72 bp. Intron splice-junction sequences all adhere to the GT---AG rule. The positions of the introns show little similarity to the intron positions in the closely related lignin peroxidase-encoding genes. The 5' upstream region of the mnp-1 gene contains a TATAA element and three inverted CCAAT elements (ATTGG) at nt positions -81, -181, -195, and -304, respectively, relative to the start codon. In addition, the mnp-1 gene contains three putative heat-shock (HS) elements similar to the consensus C--GAA--TTC--G sequence, and two consensus metal response elements located within 500 bp upstream from the start codon. Furthermore, Northern-blot analysis demonstrates that mnp gene transcription is regulated by HS.

Amino Acid Sequence↗

PubMed1990

Lignin peroxidase compounds II and III. Spectral and kinetic characterization of reactions with peroxides.

Stopped-flow techniques were used to investigate the kinetics of the reaction of lignin peroxidase compounds II and III (LiPII and LiPIII) with peroxides. Rate data were obtained from single-turnover experiments under pseudo-first-order conditions. LiPII reacts with H2O2 or peracetic acid (AcOOH) to form a modified LiPIII, designated as LiPIII*, via a biphasic reaction. During the first phase, LiPIII is formed as an intermediate. Kinetic analysis also indicates a LiPII-peroxide complex. The first-order dissociation rate constants for the reaction of LiPII with H2O2 and AcOOH are 7.9 +/- 0.5 and 4.9 +/- 0.6 s-1, respectively. The rate of the H2O2 reaction is approximately 500 times the rate of the comparable reaction with horseradish peroxidase, suggesting it is physiologically significant. The activation energy for the formation of LiPIII is 23 kJ mol-1. During the second phase, the intermediate LiPIII is converted to LiPIII*, confirmed by analyzing the reaction of exogenously prepared LiPIII with peroxides. The second-order rate constants for the reaction of LiPIII with H2O2 and AcOOH are (3.7 +/- 0.2) x 10(2) M-1 s-1 and (2.9 +/- 0.2) x 10(2) M-1 s-1, respectively. The conversion of LiPIII to LiPIII* is reversible; the first-order rate constant for the reverse reaction is approximately (6.6 +/- 0.6) x 10(-2) s-1. The rates of both LiPIII and LiPIII* formation decrease markedly above pH 4.0. The pH dependence of these reactions is controlled by a heme-linked ionizable group of pK alpha congruent to 4.2.

Basidiomycota↗

PubMed1990

Lignin peroxidase compound III. Mechanism of formation and decomposition.

Lignin peroxidase compound III (LiPIII) was prepared via three procedures: (a) ferrous LiP + O2 (LiPIIIa), (b) ferric LiP + O2-. (LiPIIIb), and (c) LiP compound II + excess H2O2 followed by treatment with catalase (LiPIIIc). LiPIIIa, b, and c each have a Soret maximum at approximately 414 nm and visible bands at 543 and 578 nm. LiPIIIa, b, and c each slowly reverted to native ferric LiP, releasing stoichiometric amounts of O2-. in the process. Electronic absorption spectra of LiPIII reversion to the native enzyme displayed isosbestic points in the visible region at 470, 525, and 597 nm, suggesting a single-step reversion with no intermediates. The LiPIII reversion reactions obeyed first-order kinetics with rate constants of approximately 1.0 X 10(-3) s-1. In the presence of excess peroxide, at pH 3.0, native LiP, LiPII, and LiPIIIa, b, and c are all converted to a unique oxidized species (LiPIII*) with a spectrum displaying visible bands at 543 and 578 nm, but with a Soret maximum at 419 nm, red-shifted 5 nm from that of LiPIII. LiPIII* is bleached and inactivated in the presence of excess H2O2 via a biphasic process. The fast first phase of this bleaching reaction obeys second-order kinetics, with a rate constant of 1.7 X 10(1) M-1 s-1. Addition of veratryl alcohol to LiPIII* results in its rapid reversion to the native enzyme, via an apparent one-step reaction that obeys second-order kinetics with a rate constant of 3.5 X 10(1) M-1 s-1. Stoichiometric amounts of O2-. are released during this reaction. When this reaction was run under conditions that prevented further reactions, HPLC analysis of the products demonstrated that veratryl alcohol was not oxidized. These results suggest that the binding of veratryl alcohol to LiPIII* displaces O2-., thus returning the enzyme to its native state. In contrast, the addition of veratryl alcohol to LiPIII did not affect the rate of spontaneous reversion of LiPIII to the native enzyme.

Agaricales↗

PubMed1990

Inactivation of lignin peroxidase by phenylhydrazine and sodium azide.

Lignin peroxidase (LiP) is rapidly inactivated in a concentration-dependent manner by H2O2 and either phenylhydrazine or sodium azide. Full inactivation of isozyme 2b (H8) requires approximately 50 eq of phenylhydrazine or 80 eq of sodium azide. Anaerobic incubation of isozyme 2b with [14C]phenylhydrazine and H2O2 results in 77% loss of catalytic activity and covalent binding of 0.45 mol radiolabel/mol of enzyme. Comparable but not identical results are obtained with an isozyme mixture. A lag period is observed before the peroxidative activity can be measured when an aliquot of an incubation with sodium azide is diluted into the mixture used to assay residual catalytic activity. This lag is associated with reversible accumulation of a catalytically inert species with a Compound III-like spectrum. No meso-phenyl, iron-phenyl, or N-phenyl adducts are formed with phenylhydrazine but a low yield of what appears to be delta-meso-azidoheme is obtained with sodium azide. LiP is thus less susceptible to meso heme additions and more susceptible to oxidative heme degradation than horseradish peroxidase. The data suggest that the active of LiP resembles the closed structure of horseradish peroxidase more than it does the open structure of the globins, catalase, chloroperoxidase, or cytochrome P450.

Azides↗

PubMed1990

Manganese regulates expression of manganese peroxidase by Phanerochaete chrysosporium.

The appearance of manganese peroxidase (MnP) activity in nitrogen-limited cultures of Phanerochaete chrysosporium is dependent on the presence of manganese. Cultures grown in the absence of Mn developed normally and produced normal levels of the secondary metabolite veratryl alcohol but produced no MnP activity. Immunoblot analysis indicated that appearance of MnP protein in the extracellular medium was also dependent on the presence of Mn. Intracellular MnP protein was detectable only in cells grown in the presence of Mn. MnP mRNA was detected by Northern (RNA) blot analysis only in cells grown in the presence of Mn. If Mn was added to 4-day-old nitrogen-limited Mn-deficient cultures, extracellular MnP activity appeared after 6 h and reached a maximum after 18 h. Both actinomycin D and cycloheximide inhibited the induction of MnP activity by Mn. These results indicate that Mn, the substrate of the enzyme, is involved in the transcriptional regulation of the MnP gene.

Basidiomycota↗

PubMed1989

Thiol-mediated oxidation of nonphenolic lignin model compounds by manganese peroxidase of Phanerochaete chrysosporium.

In the presence of MnII, H2O2, and glutathione (GSH), manganese peroxidase oxidized veratryl alcohol (I) to veratraldehyde (IV). Anisyl alcohol (II) and benzyl alcohol (III) were also oxidized by this system to their corresponding aldehydes (V and VI). In the presence of GSH, chemically prepared MnIII or gamma-irradiation also catalyzed the oxidation of I, II, and III to IV, V, and VI, respectively. GSH and dithiothreitol rapidly reduced MnIII to MnII in the absence of aromatic substrates and the dithiothreitol was oxidized to its disulfide (4,5-dihydroxyl-1,2-dithiane). These results indicate that the thiol is oxidized by enzyme-generated MnIII to a thiyl radical. The latter abstracts a hydrogen from the substrate, forming a benzylic radical which reacts with another thiyl radical to yield an intermediate which decomposes to the benzaldehyde product. In the presence of MnII, GSH, and H2O2, manganese peroxidase also oxidized 1-(4-ethoxy-3-methoxy-phenyl)-2-(4'-hydroxymethyl-2'-methoxyphenoxy)- 1,3-dihydroxypropane (XII) to yield vanillyl alcohol (VII), vanillin (VIII), 1-(4-ethoxy-3-methoxyphenyl)-1,3-dihydroxypropane (XVI), 1-(4-ethoxy-3-methoxyphenyl)-1-oxo-3-hydroxypropane (XIX), and several C alpha oxidized dimeric products. Abstraction of the C alpha (A ring) hydrogen of the dimer (XII) yields a benzylic radical, leading to C beta oxygen ether cleavage. The resultant intermediates yield the ketone (XIX) and vanillyl alcohol (VII) or vanillin (VIII). Alternatively, benzylic radical formation at the C' alpha position (B ring) leads to radical cleavage, yielding a quinone methide and a C beta radical, which yield vanillin and the 1,3-diol (XVI), respectively. In these reactions, MnIII oxidizes a thiol to a thiyl radical which subsequently abstracts a hydrogen from the substrate to form a benzylic radical. The latter undergoes nonenzymatic reactions to yield the final products.

Aerobiosis↗