Electroenzymatic oxidation of veratryl alcohol by lignin peroxidase

This paper reports the formation of veratraldehyde by electroenzymatic oxidation of veratryl alcohol (3,4-dimethoxybenzyl alcohol) hybridizing both electrochemical and enzymatic reactions and using lignin peroxidase. The novel electroenzymatic method was found to be effective for replacement of hydrogen peroxide by an electrochemical reactor, which is essential for enzyme activity of lignin peroxidase. The effects of operating parameters such as enzyme dosage, pH, and electric potential were investigated. Further, the kinetics of veratryl alcohol oxidation in an electrochemical reactor were compared to oxidation when hydrogen peroxide was supplied externally.     

A critical study of lignin peroxidase activity assay by veratryl alcohol oxidation

Summary The effects of various parameters on Phanerochaete chrysosporium lignin peroxidase activity as obtained in ligninase assay based on the oxidation of veratryl alcohol were investigated. Marked differences in the ligninase activity were observed when the temperature and pH were varied within the ranges of 23 to 37°C and 2.5 to 4.0, respectively, reported to have been used by various research groups. Further, both veratryl alcohol, and hydrogen peroxide concentration had a significant effect on ligninase activity.     

On the mechanism of inhibition of the veratryl alcohol oxidase activity of lignin peroxidase H2 by EDTA.

The mechanism of inhibition of the veratryl alcohol oxidase activity of lignin peroxidase H2 (LiPH2) by EDTA was investigated. It was found that EDTA was decarboxylated and that cytochrome c, nitro blue tetrazolium, ferric iron, and molecular oxygen were reduced in a reaction mixture containing LiPH2, H2O2, veratryl alcohol, and EDTA. The reductive activity observed with LiPH2 followed first order kinetics with respect to the concentration of EDTA. Stoichiometry studies showed that in the presence of sufficient EDTA, 1.7 mol of ferric iron were reduced per mole of H2O2 added to the reaction mixture. Superoxide- and EDTA-derived radicals were detected by ESR spin trapping upon incubation of LiPH2 with H2O2, veratryl alcohol, and EDTA. The Km values of veratryl alcohol and H2O2 remained the same for both the oxidative and reductive activities of LiPH2. Reductive activity was also observed with LiPH2 and EDTA using other free radical mediators in the place of veratryl alcohol, such as 1,4-dimethoxybenzene, 1,2,3- and 1,2,4-trimethoxybenzenes, and 1,2,4,5-tetramethoxybenzene. EDTA reduced the cation radical of 1,2,4,5-tetramethoxybenzene formed by LiPH2 in the presence of H2O2. Hence, it is proposed that the apparent inhibition of the veratryl alcohol oxidase activity of LiPH2 by EDTA is due to the reduction of the veratryl alcohol cation radical intermediate back to veratryl alcohol by EDTA. The reduction of cytochrome c, nitro blue tetrazolium, ferric ion, and molecular oxygen appears to be mediated by the EDTA radical formed by reduction of the veratryl alcohol cation radical.     

Kinetic studies on veratryl alcohol transformation by horseradish peroxidase

A number of peroxidases, such as lignin peroxidase and manganese peroxidase have proved to be useful for industrial applications. Some studies on the effects of temperature and pH stability have been carried out. It is known that veratryl alcohol increases their stability in the range 28-50 degrees C and is oxidized, leading to veratryl aldehyde formation. Similar results with horseradish peroxidase (HRP) in the presence of cofactors were found, but the oxidation of veratryl alcohol in the absence of cofactors was extremely labile at acid pH and inactivated in a few minutes. Considering the growing industrial application of HRP, knowledge of its stability and denaturation kinetics is required. In this study, horseradish peroxidase pool (HRP-VI) and its isoenzymes HRP-VIII (acid) and HRP-IX (basic) have been shown to catalyze the oxidation of veratryl alcohol to veratryl aldehyde in the presence of hydrogen peroxide at pH 5.8 in the 35-45 degrees C range and in the absence of any cofactors. Heat and pH denaturation experiments in the presence and absence of veratryl alcohol incubation were conducted with HRP-VI and HRP-IX isoenzymes. HRP-IX was the most active isoenzyme acting on veratryl alcohol but HRP-VI was the most stable for the temperature range tested. At 35 degrees C the HRP pool presented decay constant (Kd) values of 5.5 x 10(-2) h(-1) and 1.4 10(-2) h(-1) in the absence and presence of veratryl alcohol, respectively, with an effective ratio of 3.9. These results present a new feature of peroxidases that opens one more interesting application of HRP to industrial processes.     

Reactivity of manganese peroxidase: site-directed mutagenesis of residues in proximity to the porphyrin ring

The purpose of this study was to determine the effect of heme pocket hydrophobicity on the reactivity of manganese peroxidase. Residues within 5 A of the heme active site were identified. From this group, Leu169 and Ser172 were selected and mutated to Phe and Ala, respectively. The mutant proteins were then characterized by steady-state kinetics. Whereas the Leu169Phe mutation had little, if any, effect on activity, the Ser172Ala mutation decreased kcat and also the specificity constant (kcat/Km) for Mn2+, but not H2O2. Transient-state studies indicated that the mutation affected only the reactions of compound II. These results indicate that compound II is the most sensitive to changes in the heme environment.     

Aromatic ring oxidation of vanillyl and veratryl alcohols by Lentinus edodes: possible artifacts in the lignin peroxidase and veratryl alcohol oxidase assays

The degradation pathway of vanillyl and veratryl alcohol by Lentinus edodes extracellular enzymes was studied. In both cases several products of side chain oxidation and aromatic ring cleavage were isolated and characterized. We have observed that the products from veratryl alcohol degradation by Lentinus edodes are quite different from those isolated from incubations with other white-rot fungi which have veraraldehyde as the major product, in fact, this compound is not produced as final metabolite in L. edodes incubations. This behaviour could explain the apparent absence of lignin peroxidase and veratryl alcohol oxidase activities in L. edodes cultures, since such activities are usually measured by monitoring veratraldehyde formation during the veratryl alcohol oxidation; thus, it is suggested that additional assay methods should be developed, with preferably direct observation of aromatic ring oxidation products.     

The mediation of veratryl alcohol in oxidations promoted by lignin peroxidase: the lifetime of veratryl alcohol radical cation

The kinetics of decay of veratryl alcohol radical cation, generated by cerium(IV) ammonium nitrate induced oxidation of veratryl alcohol, have been followed spectrophotometrically in a stopped-flow apparatus. In acidic aqueous acetonitrile the radical cation was found to decay by a first-order process, due to deprotonation from the alpha-carbon leading to an alpha-hydroxybenzyl radical with the rate constant of 17.1+/-0.5 s(-1). This value is in full agreement with those obtained by pulse radiolysis studies but much lower than the value (1.2x10(3) s(-1)) indirectly determined by EPR experiments. The implications of these results with respect to the possible role of veratryl alcohol as a mediator in the oxidative biodegradation of lignin catalysed by lignin peroxidase are discussed.     

Improvement of the thermostability and enzymatic activity of cholesterol oxidase by site-directed mutagenesis

Site-directed mutagenesis was applied to enhance the thermostability and enzymatic activity of cholesterol oxidase (ChOx) isolated from Brevibacterium sp. Three amino acid residues (Q153E, F128L, and S143H) located near the FAD-binding site of the enzyme were substituted based on structural analysis. The specific activity of the two-sites mutant Q153E/F128L increased by 11.6% and the relative activity increased by 47% when grown for 2 h at 50°C. This mutant is a potential industrial strain for producing ChOx.     

利用定点突变法研究精氨酸脱亚胺酶活性的影响机制

精氨酸脱亚胺酶(ADI)是一种针对精氨酸缺陷型癌症(如:肝癌、黑素瘤)的新药,目前处于临床三期试验。文中通过定点突变技术分析了精氨酸脱亚胺酶的特定氨基酸位点对酶活力的影响机制。针对已报道的关键氨基酸残基A128、H404、I410,采用QuikChange法进行定点突变,获得ADI突变株M1(A128T)、M2(H404R)、M3(I410L)和M4(A128T/H404R)。将突变株在大肠杆菌BL21(DE3)中进行重组表达,并对纯化获得的突变蛋白进行酶学性质研究。结果表明,突变位点A128T和H404R对ADI最适pH的提高,生理中性(pH 7.4)条件下的酶活力和稳定性的提高,以及Km值的降低均具有显著的作用。研究结果为阐明ADI的酶活力影响机制和蛋白质的理性改造提供了一定的依据。     

Production of a perillyl alcohol dehydrogenase by site-directed mutagenesis of a benzyl alcohol dehydrogenase

Benzyl alcohol dehydrogenase from Acinetobacter calcoaceticus oxidises a wide range of aromatic and other cyclic alcohols and it has high specificity constants for these substrates, but it does not oxidise short- or long-chain aliphatic alcohols. Mutation of an active-site arginine to a histidine can switch the substrate specificity of the enzyme so that it has a very much greater preference for perillyl alcohol than for benzyl alcohol. © Rapid Science Ltd. 1998     

Thiol and Mn(2+)-mediated oxidation of veratryl alcohol by horseradish peroxidase.

Horseradish peroxidase has been shown to catalyze the oxidation of veratryl alcohol (3,4-dimethoxybenzyl alcohol) and benzyl alcohol to the respective aldehydes in the presence of reduced glutathione, MnCl2, and an organic acid metal chelator such as lactate. The oxidation is most likely the result of hydrogen abstraction from the benzylic carbon of the substrate alcohol leading to eventual disproportionation to the aldehyde product. An aromatic cation radical intermediate, as would be formed during the oxidation of veratryl alcohol in the lignin peroxidase-H2O2 system, is not formed during the horseradish peroxidase-catalyzed reaction. In addition to glutathione, dithiothreitol, L-cysteine, and beta-mercaptoethanol are capable of promoting veratryl alcohol oxidation. Non-thiol reductants, such as ascorbate or dihydroxyfumarate (known substrates of horseradish peroxidase), do not support oxidation of veratryl alcohol. Spectral evidence indicates that horseradish peroxidase compound II is formed during the oxidation reaction. Furthermore, electron spin resonance studies indicate that glutathione is oxidized to the thiyl radical. However, in the absence of Mn2+, the thiyl radical is unable to promote the oxidation of veratryl alcohol. In addition, Mn3+ is unable to promote the oxidation of veratryl alcohol in the absence of glutathione. These results suggest that the ultimate oxidant of veratryl alcohol is a Mn(3+)-GSH or Mn(2+)-GS. complex (where GS. is the glutathiyl radical).     

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)     

Improving the activity and stability of thermolysin by site-directed mutagenesis

In previous site-directed mutagenesis study on thermolysin, mutations which increase the catalytic activity or the thermal stability have been identified. In this study, we attempted to generate highly active and stable thermolysin by combining the mutations so far revealed to be effective. Three mutant enzymes, L144S (Leu144 in the central alpha-helix located at the bottom of the active site cleft is replaced with Ser), G8C/N60C/S65P (Gly8, Asn60, and Ser65 in the N-terminal region are replaced with Cys, Cys, and Pro, respectively, to introduce a disulfide bridge between the positions 8 and 60), and G8C/N60C/S65P/L144S, were constructed by site-directed mutagenesis. In the hydrolysis of N-[3-(2-furyl)acryloyl]-glycyl-L-leucine amide (FAGLA) and N-carbobenzoxy-L-aspartyl-L-phenylalanine methyl ester (ZDFM), the k(cat)/K(m) values of L144S and G8C/N60C/S65P/L144S were 5- to 10-fold higher than that of the wild-type enzyme. The rate constants for thermal inactivation at 70 degrees C and 80 degrees C of G8C/N60C/S65P and G8C/N60C/S65P/L144S decreased to 50% of that of the wild-type enzyme. These results indicate that G8C/N60C/S65P/L144S is more active and stable than the wild-type thermolysin. Thermodynamic analysis suggests that the single mutation of Leu144-->Ser and the triple mutation of Gly8-->Cys, Asn60-->Cys, and Ser65-->Pro are independent.     

Degradation of veratryl alcohol by Penicillium simplicissimum

Summary Several bacteria, yeast and fungi selectively isolated from paper-mill waste-water grew on veratryl alcohol, a key intermediate of lignin metabolism. Penicillium simplicissimum oxidized veratryl alcohol via a NAD(P)⁺-dependent veratryl alcohol dehydrogenase to veratraldehyde, which was further oxidized to veratric acid in a NAD(P)⁺-dependent reaction. Veratric-acid-grown cells contained NAD(P)H-dependent O-demethylase activity for veratrate, vanillate and isovanillate. Protocatechuate was cleaved by a protocatechuate 3,4-dioxygenase. Offprint requests to: E. de Jong     

定点突变提高土曲霉Aspergillus terreus脂肪酶的催化活性

本研究旨在利用理性设计的方法来提高来源于土曲霉Aspergillus terreus的酸性脂肪酶ATL的催化活力。通过同源比对,选择脂肪酶盖子区域和底物结合口袋域中的位点进行定点突变,得到8种ATL的突变脂肪酶。结果发现,盖子区域突变酶ATLLid与底物结合口袋域突变酶ATLV218W的催化活性显著提高。ATLLid和ATLV218W对底物对硝基苯酚月桂酸酯p-nitrophenyl laurate(p-NPL)的催化活性最高,k_(cat)值较ATL分别提高了39.37倍和50.79倍,k_(cat)/K_m值较ATL分别提高了2.85倍和8.48倍。与ATL相比,ATLLid和ATLV218W的热稳定性略有下降,最适p H为5.0,p H 4.0–8.0具有较好的稳定性,说明突变未对ATL的嗜酸耐酸特性产生影响。通过同源建模模拟及分子对接技术分析底物p-NPL与酶分子间的相互作用,解析了ATLLid和ATLV218W催化活性提高的机理。     

The roles of veratryl alcohol and nonionic surfactant in the oxidation of phenolic compounds by lignin peroxidase

Veratryl alcohol (VA) at higher concentration stimulated the lignin peroxidase (LiP)-catalyzed oxidation of phenolic compounds remarkably. This novel phenomenon was due to its competition with the phenols for the active site of the enzyme and to the high reactivity of the formed cation radical of VA (VA+*) which resulted in an additional oxidation of the phenols. The influence of the nonionic surfactant Tween 80 on the VA-enhanced LiP-catalyzed oxidation of phenols depended on its concentration. At lower concentration it had a small synergetic effect but at higher concentration it decreased the initial rate. Studies of the capillary electrophoretic behavior of LiP in the presence of Tween 80 showed that this effect was caused by the surfactant aggregation on LiP which, at higher surfactant concentrations, might impede the access of VA to its binding site on LiP and, consequently, the VA+* formation.     

Involvement of veratryl alcohol and active oxygen species in degradation of a quinone compound by lignin peroxidase

Degradation of 2-hydroxy-1,4-naphthoquinone (HNQ) by lignin peroxidase is discussed. Degradation rat was remarkably increased by an increase in veratryl alcohol concentration. Degradation is partly prevented by adding OH. scavenger (mannitol or DMSO) to the reaction mixture. Addition of O2-. scavenger (Mn2+) to the reaction mixture completely prevents the degradation. These results suggest that active oxygen species formed in the lignin peroxidase-H2O2-veratryl alcohol system play an important role in HNQ degradation.     

Generation of a biologically active, secreted form of human thyroid peroxidase by site-directed mutagenesis

Using site-directed mutagenesis, we introduced two stop codons immediately upstream of the putative transmembrane domain in human thyroid peroxidase (hTPO) cDNA, truncating the carboxyl terminus of hTPO (933 amino acids) by 85 residues. Mutated hTPO cDNA, inserted into a eukaryotic expression vector, was stably transfected into Chinese hamster ovary (CHO) cells. Immunoprecipitation of cellular 35S-methionine-labeled proteins with Hashimoto's serum revealed a 105-101 kilodalton doublet. In contrast, cells transfected with wild-type hTPO yielded a 112-105 kilodalton doublet. In pulse-chase experiments, CHO cells expressing the truncated hTPO protein secreted immunoprecipitable TPO into the culture medium after 4 h of chase, with levels accumulating progressively over a 24-h period. In contrast, CHO cells expressing wild-type hTPO released no immunoprecipitable TPO into the culture medium. The secreted, truncated form of hTPO appeared as a single band of lesser electrophoretic mobility, as opposed to the doublet expressed within cells. TPO enzymatic activity was present in conditioned media from CHO cells transfected with the mutated hTPO, but was absent in media from cells expressing wild-type hTPO. The stability of the mutated protein appeared similar to that of wild-type hTPO. In summary, we have generated a mutated, secreted form of hTPO that is enzymatically active and immunologically intact. Our data confirm the existence of a transmembrane domain in hTPO, and that hTPO is predominantly an enzyme with an extracellular orientation. The secreted form of hTPO has the potential for generating large amounts of soluble TPO protein for use in future structural and immunological studies.     

Alteration of substrate specificity of cholesterol oxidase from Streptomyces sp. by site-directed mutagenesis

Despite the structural similarities between cholesterol oxidase from Streptomyces and that from Brevibacterium, both enzymes exhibit different characteristics, such as catalytic activity, optimum pH and temperature. In attempts to define the molecular basis of differences in catalytic activity or stability, substitutions at six amino acid residues were introduced into cholesterol oxidase using site-directed mutagenesis of its gene. The amino acid substitutions chosen were based on structural comparisons of cholesterol oxidases from Streptomyces and BREVIBACTERIUM: Seven mutant enzymes were constructed with the following amino acid substitutions: L117P, L119A, L119F, V145Q, Q286R, P357N and S379T. All the mutant enzymes exhibited activity with the exception of that with the L117P mutation. The resulting V145Q mutant enzyme has low activities for all substrates examined and the S379T mutant enzyme showed markedly altered substrate specificity compared with the wild-type enzyme. To evaluate the role of V145 and S379 residues in the reaction, mutants with two additional substitutions in V145 and four in S379 were constructed. The mutant enzymes created by the replacement of V145 by Asp and Glu had much lower catalytic efficiency for cholesterol and pregnenolone as substrates than the wild-type enzyme. From previous studies and this study, the V145 residue seems to be important for the stability and substrate binding of the cholesterol oxidase. In contrast, the catalytic efficiencies (k(cat)/K(m)) of the S379T mutant enzyme for cholesterol and pregnenolone were 1.8- and 6.0-fold higher, respectively, than those of the wild-type enzyme. The enhanced catalytic efficiency of the S379T mutant enzyme for pregnenolone was due to a slightly high k(cat) value and a low K(m) value. These findings will provide several ideas for the design of more powerful enzymes that can be applied to clinical determination of serum cholesterol levels and as sterol probes.