Transforming an esterase into an enantioselective catecholase through bioconjugation of a versatile metal-chelating inhibitor.

Metal complexes introduced into protein scaffolds can generate versatile biomimetic catalysts endowed with a variety of catalytic properties. Here, we synthesized and covalently bound a bipyridinyl derivative to the active centre of an esterase to generate a biomimetic catalyst that shows catecholase activity and enantioselective catalytic oxidation of (+)-catechin.

Enzyme adaptation to habitat thermal legacy shapes the thermal plasticity of marine microbiomes.

Microbial communities respond to temperature with physiological adaptation and compositional turnover. Whether thermal selection of enzymes explains marine microbiome plasticity in response to temperature remains unresolved. By quantifying the thermal behaviour of seven functionally-independent enzyme classes (esterase, extradiol dioxygenase, phosphatase, beta-galactosidase, nuclease, transaminase, and aldo-keto reductase) in native proteomes of marine sediment microbiomes from the Irish Sea to the southern Red Sea, we record a significant effect of the mean annual temperature (MAT) on enzyme response in all cases. Activity and stability profiles of 228 esterases and 5 extradiol dioxygenases from sediment and seawater across 70 locations worldwide validate this thermal pattern. Modelling the esterase phase transition temperature as a measure of structural flexibility confirms the observed relationship with MAT. Furthermore, when considering temperature variability in sites with non-significantly different MATs, the broadest range of enzyme thermal behaviour and the highest growth plasticity of the enriched heterotrophic bacteria occur in samples with the widest annual thermal variability. These results indicate that temperature-driven enzyme selection shapes microbiome thermal plasticity and that thermal variability finely tunes such processes and should be considered alongside MAT in forecasting microbial community thermal response.

Thermophilic Carboxylesterases from Hydrothermal Vents of the Volcanic Island of Ischia Active on Synthetic and Biobased Polymers and Mycotoxins.

Hydrothermal vents are geographically widespread and host microorganisms with robust enzymes useful in various industrial applications. We examined microbial communities and carboxylesterases of two terrestrial hydrothermal vents of the volcanic island of Ischia (Italy) predominantly composed of Firmicutes, Proteobacteria, and Bacteroidota. High-temperature enrichment cultures with the polyester plastics polyhydroxybutyrate and polylactic acid (PLA) resulted in an increase of Thermus and Geobacillus species and to some extent Fontimonas and Schleiferia species. The screening at 37 to 70°C of metagenomic fosmid libraries from above enrichment cultures identified three hydrolases (IS10, IS11, and IS12), all derived from yet-uncultured Chloroflexota and showing low sequence identity (33 to 56%) to characterized enzymes. Enzymes expressed in Escherichia coli exhibited maximal esterase activity at 70 to 90°C, with IS11 showing the highest thermostability (90% activity after 20-min incubation at 80°C). IS10 and IS12 were highly substrate promiscuous and hydrolyzed all 51 monoester substrates tested. Enzymes were active with PLA, polyethylene terephthalate model substrate, and mycotoxin T-2 (IS12). IS10 and IS12 had a classical α/ß-hydrolase core domain with a serine hydrolase catalytic triad (Ser155, His280, and Asp250) in their hydrophobic active sites. The crystal structure of IS11 resolved at 2.92 Å revealed the presence of a N-terminal ß-lactamase-like domain and C-terminal lipocalin domain. The catalytic cleft of IS11 included catalytic Ser68, Lys71, Tyr160, and Asn162, whereas the lipocalin domain enclosed the catalytic cleft like a lid and contributed to substrate binding. Our study identified novel thermotolerant carboxylesterases with a broad substrate range, including polyesters and mycotoxins, for potential applications in biotechnology. IMPORTANCE High-temperature-active microbial enzymes are important biocatalysts for many industrial applications, including recycling of synthetic and biobased polyesters increasingly used in textiles, fibers, coatings and adhesives. Here, we identified three novel thermotolerant carboxylesterases (IS10, IS11, and IS12) from high-temperature enrichment cultures from Ischia hydrothermal vents and incubated with biobased polymers. The identified metagenomic enzymes originated from uncultured Chloroflexota and showed low sequence similarity to known carboxylesterases. Active sites of IS10 and IS12 had the largest effective volumes among the characterized prokaryotic carboxylesterases and exhibited high substrate promiscuity, including hydrolysis of polyesters and mycotoxin T-2 (IS12). Though less promiscuous than IS10 and IS12, IS11 had a higher thermostability with a high temperature optimum (80 to 90°C) for activity and hydrolyzed polyesters, and its crystal structure revealed an unusual lipocalin domain likely involved in substrate binding. The polyesterase activity of these enzymes makes them attractive candidates for further optimization and potential application in plastics recycling.

The Mobility of the Cap Domain Is Essential for the Substrate Promiscuity of a Family IV Esterase from Sorghum Rhizosphere Microbiome.

Metagenomics offers the possibility to screen for versatile biocatalysts. In this study, the microbial community of the Sorghum bicolor rhizosphere was spiked with technical cashew nut shell liquid, and after incubation, the environmental DNA (eDNA) was extracted and subsequently used to build a metagenomic library. We report the biochemical features and crystal structure of a novel esterase from the family IV, EH0, retrieved from an uncultured sphingomonad after a functional screen in tributyrin agar plates. EH0 (optimum temperature [Topt], 50°C; melting temperature [Tm], 55.7°C; optimum pH [pHopt], 9.5) was stable in the presence of 10 to 20% (vol/vol) organic solvents and exhibited hydrolytic activity against p-nitrophenyl esters from acetate to palmitate, preferably butyrate (496 U mg-1), and a large battery of 69 structurally different esters (up to 30.2 U mg-1), including bis(2-hydroxyethyl)-terephthalate (0.16 ± 0.06 U mg-1). This broad substrate specificity contrasts with the fact that EH0 showed a long and narrow catalytic tunnel, whose access appears to be hindered by a tight folding of its cap domain. We propose that this cap domain is a highly flexible structure whose opening is mediated by unique structural elements, one of which is the presence of two contiguous proline residues likely acting as possible hinges, which together allow for the entrance of the substrates. Therefore, this work provides a new role for the cap domain, which until now was thought to be an immobile element that contained hydrophobic patches involved in substrate prerecognition and in turn substrate specificity within family IV esterases. IMPORTANCE A better understanding of structure-function relationships of enzymes allows revelation of key structural motifs or elements. Here, we studied the structural basis of the substrate promiscuity of EH0, a family IV esterase, isolated from a sample of the Sorghum bicolor rhizosphere microbiome exposed to technical cashew nut shell liquid. The analysis of EH0 revealed the potential of the sorghum rhizosphere microbiome as a source of enzymes with interesting properties, such as pH and solvent tolerance and remarkably broad substrate promiscuity. Its structure resembled those of homologous proteins from mesophilic Parvibaculum and Erythrobacter spp. and hyperthermophilic Pyrobaculum and Sulfolobus spp. and had a very narrow, single-entry access tunnel to the active site, with access controlled by a capping domain that includes a number of nonconserved proline residues. These structural markers, distinct from those of other substrate-promiscuous esterases, can help in tuning substrate profiles beyond tunnel and active site engineering.

Crystal structure of a family VIII ß-lactamase fold hydrolase reveals the molecular mechanism for its broad substrate scope.

Family VIII esterases present similarities to class C ß-lactamases, which show nucleophilic serines located at the S-X-X-K motif instead of the G-X-S-X-G or G-D-S-(L) motif shown by other carboxylesterase families. Here, we report the crystal structure of a novel family VIII (subfamily VIII. I) esterase (EH7 ; denaturing temperature, 52.6 ± 0.3 °C; pH optimum 7.0-9.0) to deepen its broad substrate range. Indeed, the analysis of the substrate specificity revealed its capacity to hydrolyse nitrocefin as a model chromogenic cephalosporin substrate (40.4 ± 11.4 units·g-1 ), and a large battery of 66 structurally different esters (up to 1730 min-1 ), including bis(2-hydroxyethyl)-terephthalate (241.7 ± 8.5 units·g-1 ) and the mycotoxin T-2 (1220 ± 52 units·g-1 ). It also showed acyltransferase activity through the synthesis of benzyl 3-oxobutanoate (40.4 ± 11.4 units·g-1 ) from benzyl alcohol and vinyl acetoacetate. Such a broad substrate scope is rare among family VIII esterases and lipolytic enzymes. Structural analyses of free and substrate-bound forms of this homooctamer esterase suggest that EH7 presents a more opened and exposed S1 site having no steric hindrance for the entrance of substrates to the active site, more flexible R1, R2 and R3 regions allowing for the binding of a wide spectrum of substrates into the active site, and small residues in the conserved motif Y-X-X containing the catalytic Tyr enabling the entrance of large substrates. These unique structural elements in combination with docking experiments allowed us to gain valuable insights into the substrate specificity of this esterase and possible others belonging to family VIII.

A Plurizyme with Transaminase and Hydrolase Activity Catalyzes Cascade Reactions.

Engineering dual-function single polypeptide catalysts with two abiotic or biotic catalytic entities (or combinations of both) supporting cascade reactions is becoming an important area of enzyme engineering and catalysis. Herein we present the development of a PluriZyme, TR2 E2 , with efficient native transaminase (kcat : 69.49±1.77 min-1 ) and artificial esterase (kcat : 3908-0.41 min-1 ) activities integrated into a single scaffold, and evaluate its utility in a cascade reaction. TR2 E2 (pHopt : 8.0-9.5; Topt : 60-65 °C) efficiently converts methyl 3-oxo-4-(2,4,5-trifluorophenyl)butanoate into 3-(R)-amino-4-(2,4,5-trifluorophenyl)butanoic acid, a crucial intermediate for the synthesis of antidiabetic drugs. The reaction proceeds through the conversion of the ß-keto ester into the ß-keto acid at the hydrolytic site and subsequently into the ß-amino acid (e.e. >99 %) at the transaminase site. The catalytic power of the TR2 E2 PluriZyme was proven with a set of ß-keto esters, demonstrating the potential of such designs to address bioinspired cascade reactions.

Structure and evolutionary trace-assisted screening of a residue swapping the substrate ambiguity and chiral specificity in an esterase.

Our understanding of enzymes with high substrate ambiguity remains limited because their large active sites allow substrate docking freedom to an extent that seems incompatible with stereospecificity. One possibility is that some of these enzymes evolved a set of evolutionarily fitted sequence positions that stringently allow switching substrate ambiguity and chiral specificity. To explore this hypothesis, we targeted for mutation a serine ester hydrolase (EH3) that exhibits an impressive 71-substrate repertoire but is not stereospecific (e.e. 50%). We used structural actions and the computational evolutionary trace method to explore specificity-swapping sequence positions and hypothesized that position I244 was critical. Driven by evolutionary action analysis, this position was substituted to leucine, which together with isoleucine appears to be the amino acid most commonly present in the closest homologous sequences (max. identity, ca. 67.1%), and to phenylalanine, which appears in distant homologues. While the I244L mutation did not have any functional consequences, the I244F mutation allowed the esterase to maintain a remarkable 53-substrate range while gaining stereospecificity properties (e.e. 99.99%). These data support the possibility that some enzymes evolve sequence positions that control the substrate scope and stereospecificity. Such residues, which can be evolutionarily screened, may serve as starting points for further designing substrate-ambiguous, yet chiral-specific, enzymes that are greatly appreciated in biotechnology and synthetic chemistry.

Promiscuous Esterases Counterintuitively Are Less Flexible than Specific Ones.

Understanding mechanisms of promiscuity is increasingly important from a fundamental and application point of view. As to enzyme structural dynamics, more promiscuous enzymes generally have been recognized to also be more flexible. However, examples for the opposite received much less attention. Here, we exploit comprehensive experimental information on the substrate promiscuity of 147 esterases tested against 96 esters together with computationally efficient rigidity analyses to understand the molecular origin of the observed promiscuity range. Unexpectedly, our data reveal that promiscuous esterases are significantly less flexible than specific ones, are significantly more thermostable, and have a significantly increased specific activity. These results may be reconciled with a model according to which structural flexibility in the case of specific esterases serves for conformational proofreading. Our results signify that an esterase sequence space can be screened by rigidity analyses for promiscuous esterases as starting points for further exploration in biotechnology and synthetic chemistry.

Crystal structures of a novel family IV esterase in free and substrate-bound form.

Bacterial lipolytic enzymes of family IV are homologs of the mammalian hormone-sensitive lipases (HSL) and have been successfully used for various biotechnological applications. The broad substrate specificity and ability for enantio-, regio-, and stereoselective hydrolysis are remarkable features of enzymes from this class. Many crystal structures are available for esterases and lipases, but structures of enzyme-substrate or enzyme-inhibitor complexes are less frequent although important to understand the molecular basis of enzyme-substrate interaction and to rationalize biochemical enzyme characteristics. Here, we report on the structures of a novel family IV esterase isolated from a metagenomic screen, which shows a broad substrate specificity. We solved the crystal structures in the apo form and with a bound substrate analogue at 1.35 and 1.81 Å resolution, respectively. This enzyme named PtEst1 hydrolyzed more than 60 out 96 structurally different ester substrates thus being substrate promiscuous. Its broad substrate specificity is in accord with a large active site cavity, which is covered by an α-helical cap domain. The substrate analogue methyl 4-methylumbelliferyl hexylphosphonate was rapidly hydrolyzed by the enzyme leading to a complete inactivation caused by covalent binding of phosphinic acid to the catalytic serine. Interestingly, the alcohol leaving group 4-methylumbelliferone was found remaining in the active site cavity, and additionally, a complete inhibitor molecule was found at the cap domain next to the entrance of the substrate tunnel. This unique situation allowed gaining valuable insights into the role of the cap domain for enzyme-substrate interaction of esterases belonging to family IV. DATABASE: Structural data of PtEst1 are available in the worldwide protein data bank (https://www.rcsb.org) under the accession codes: 6Z68 (apo-PtEst1) and 6Z69 (PtEst1-inhibitor complex).

Tuning the Properties of Natural Promiscuous Enzymes by Engineering Their Nano-environment.

Owing to their outstanding catalytic properties, enzymes represent powerful tools for carrying out a wide range of (bio)chemical transformations with high proficiency. In this context, enzymes with high biocatalytic promiscuity are somewhat neglected. Here, we demonstrate that a meticulous modification of a synthetic shell that surrounds an immobilized enzyme possessing broad substrate specificity allows the resulting nanobiocatalyst to be endowed with enantioselective properties while maintaining a high level of substrate promiscuity. Our results show that control of the enzyme nano-environment enables tuning of both substrate specificity and enantioselectivity. Further, we demonstrate that our strategy of enzyme supramolecular engineering allows the enzyme to be endowed with markedly enhanced stability in an organic solvent (i.e., acetonitrile). The versatility of the method was assessed with two additional substrate-promiscuous and structurally different enzymes, for which improvements in enantioselectivity and stability were confirmed. We expect this method to promote the use of supramolecularly engineered promiscuous enzymes in industrially relevant biocatalytic processes.

Organic-Solvent-Tolerant Carboxylic Ester Hydrolases for Organic Synthesis.

Biocatalysis has emerged as an important tool in synthetic organic chemistry enabling the chemical industry to execute reactions with high regio- or enantioselectivity and under usually mild reaction conditions while avoiding toxic waste. Target substrates and products of reactions catalyzed by carboxylic ester hydrolases are often poorly water soluble and require organic solvents, whereas enzymes are evolved by nature to be active in cells, i.e., in aqueous rather than organic solvents. Therefore, biocatalysts that withstand organic solvents are urgently needed. Current strategies to identify such enzymes rely on laborious tests carried out by incubation in different organic solvents and determination of residual activity. Here, we describe a simple assay useful for screening large libraries of carboxylic ester hydrolases for resistance and activity in water-miscible organic solvents. We have screened a set of 26 enzymes, most of them identified in this study, with four different water-miscible organic solvents. The triglyceride tributyrin was used as a substrate, and fatty acids released by enzymatic hydrolysis were detected by a pH shift indicated by the indicator dye nitrazine yellow. With this strategy, we succeeded in identifying a novel highly organic-solvent-tolerant esterase from Pseudomonas aestusnigri In addition, the newly identified enzymes were tested with sterically demanding substrates, which are common in pharmaceutical intermediates, and two enzymes from Alcanivorax borkumensis were identified which outcompeted the gold standard ester hydrolase CalB from Candida antarcticaIMPORTANCE Major challenges hampering biotechnological applications of esterases include the requirement to accept nonnatural and chemically demanding substrates and the tolerance of the enzymes toward organic solvents which are often required to solubilize such substrates. We describe here a high-throughput screening strategy to identify novel organic-solvent-tolerant carboxylic ester hydrolases (CEs). Among these enzymes, CEs active against water-insoluble bulky substrates were identified. Our results thus contribute to fostering the identification and biotechnological application of CEs.

Bioprospecting Reveals Class III ω-Transaminases Converting Bulky Ketones and Environmentally Relevant Polyamines.

Amination of bulky ketones, particularly in (R) configuration, is an attractive chemical conversion; however, known ω-transaminases (ω-TAs) show insufficient levels of performance. By applying two screening methods, we discovered 10 amine transaminases from the class III ω-TA family that were 38% to 76% identical to homologues. We present examples of such enzymes preferring bulky ketones over keto acids and aldehydes with stringent (S) selectivity. We also report representatives from the class III ω-TAs capable of converting (R) and (S) amines and bulky ketones and one that can convert amines with longer alkyl substituents. The preference for bulky ketones was associated with the presence of a hairpin region proximal to the conserved Arg414 and residues conforming and close to it. The outward orientation of Arg414 additionally favored the conversion of (R) amines. This configuration was also found to favor the utilization of putrescine as an amine donor, so that class III ω-TAs with Arg414 in outward orientation may participate in vivo in the catabolism of putrescine. The positioning of the conserved Ser231 also contributes to the preference for amines with longer alkyl substituents. Optimal temperatures for activity ranged from 45 to 65°C, and a few enzymes retained ≥50% of their activity in water-soluble solvents (up to 50% [vol/vol]). Hence, our results will pave the way to design, in the future, new class III ω-TAs converting bulky ketones and (R) amines for the production of high-value products and to screen for those converting putrescine.IMPORTANCE Amine transaminases of the class III ω-TAs are key enzymes for modification of chemical building blocks, but finding those capable of converting bulky ketones and (R) amines is still challenging. Here, by an extensive analysis of the substrate spectra of 10 class III ω-TAs, we identified a number of residues playing a role in determining the access and positioning of bulky ketones, bulky amines, and (R)- and (S) amines, as well as of environmentally relevant polyamines, particularly putrescine. The results presented can significantly expand future opportunities for designing (R)-specific class III ω-TAs to convert valuable bulky ketones and amines, as well as for deepening the knowledge into the polyamine catabolic pathways.

Functional-Based Screening Methods for Detecting Esterase and Lipase Activity Against Multiple Substrates.

Functional screens have been extensively used for searching native enzymes or mutant variants in clone libraries. Esterases and lipases are the most retrieved enzymes, because they are within the more demanded industrial enzymes and because a number of simple and generic screening methods can be applied for their screen. Here, we describe the use of a generic pH indicator assay protocol which unambiguously allows detecting in high-throughput manner esterase and lipase activity and quantifying specific activities using an ester concentration above 0.5 mM. The described method is simple and generic to allow the selection of esterases and lipases targeting desired esters.

Rational Engineering of Multiple Active Sites in an Ester Hydrolase.

Effects of altering the properties of an active site in an enzymatic homogeneous catalyst have been extensively reported. However, the possibility of increasing the number of such sites, as commonly done in heterogeneous catalytic materials, remains unexplored, particularly because those have to accommodate appropriate residues in specific configurations. This possibility was investigated by using a serine ester hydrolase as the target enzyme. By using the Protein Energy Landscape Exploration software, which maps ligand diffusion and binding, we found a potential binding pocket capable of holding an extra catalytic triad and oxyanion hole contacts. By introducing two mutations, this binding pocket became a catalytic site. Its substrate specificity, substrate preference, and catalytic activity were different from those of the native site of the wild type ester hydrolase and other hydrolases, due to the differences in the active site architecture. Converting the binding pocket into an extra catalytic active site was proven to be a successful approach to create a serine ester hydrolase with two functional reactive groups. Our results illustrate the accuracy and predictive nature of modern modeling techniques, opening novel catalytic opportunities coming from the presence of different catalytic environments in single enzymes.

Determinants and Prediction of Esterase Substrate Promiscuity Patterns.

Esterases receive special attention because of their wide distribution in biological systems and environments and their importance for physiology and chemical synthesis. The prediction of esterases' substrate promiscuity level from sequence data and the molecular reasons why certain such enzymes are more promiscuous than others remain to be elucidated. This limits the surveillance of the sequence space for esterases potentially leading to new versatile biocatalysts and new insights into their role in cellular function. Here, we performed an extensive analysis of the substrate spectra of 145 phylogenetically and environmentally diverse microbial esterases, when tested with 96 diverse esters. We determined the primary factors shaping their substrate range by analyzing substrate range patterns in combination with structural analysis and protein-ligand simulations. We found a structural parameter that helps rank (classify) the promiscuity level of esterases from sequence data at 94% accuracy. This parameter, the active site effective volume, exemplifies the topology of the catalytic environment by measuring the active site cavity volume corrected by the relative solvent accessible surface area (SASA) of the catalytic triad. Sequences encoding esterases with active site effective volumes (cavity volume/SASA) above a threshold show greater substrate spectra, which can be further extended in combination with phylogenetic data. This measure provides also a valuable tool for interrogating substrates capable of being converted. This measure, found to be transferred to phosphatases of the haloalkanoic acid dehalogenase superfamily and possibly other enzymatic systems, represents a powerful tool for low-cost bioprospecting for esterases with broad substrate ranges, in large scale sequence data sets.

Catalytic surface radical in dye-decolorizing peroxidase: a computational, spectroscopic and site-directed mutagenesis study.

Dye-decolorizing peroxidase (DyP) of Auricularia auricula-judae has been expressed in Escherichia coli as a representative of a new DyP family, and subjected to mutagenic, spectroscopic, crystallographic and computational studies. The crystal structure of DyP shows a buried haem cofactor, and surface tryptophan and tyrosine residues potentially involved in long-range electron transfer from bulky dyes. Simulations using PELE (Protein Energy Landscape Exploration) software provided several binding-energy optima for the anthraquinone-type RB19 (Reactive Blue 19) near the above aromatic residues and the haem access-channel. Subsequent QM/MM (quantum mechanics/molecular mechanics) calculations showed a higher tendency of Trp-377 than other exposed haem-neighbouring residues to harbour a catalytic protein radical, and identified the electron-transfer pathway. The existence of such a radical in H2O2-activated DyP was shown by low-temperature EPR, being identified as a mixed tryptophanyl/tyrosyl radical in multifrequency experiments. The signal was dominated by the Trp-377 neutral radical contribution, which disappeared in the W377S variant, and included a tyrosyl contribution assigned to Tyr-337 after analysing the W377S spectra. Kinetics of substrate oxidation by DyP suggests the existence of high- and low-turnover sites. The high-turnover site for oxidation of RB19 (k(cat) > 200 s⁻¹) and other DyP substrates was assigned to Trp-377 since it was absent from the W377S variant. The low-turnover site/s (RB19 k(cat) ~20 s⁻¹) could correspond to the haem access-channel, since activity was decreased when the haem channel was occluded by the G169L mutation. If a tyrosine residue is also involved, it will be different from Tyr-337 since all activities are largely unaffected in the Y337S variant.

Heterologous expression and physicochemical characterization of a fungal dye-decolorizing peroxidase from Auricularia auricula-judae.

An efficient heterologous expression system for Auricularia auricula-judae dye-decolorizing peroxidase (DyP) has been constructed. DNA coding for the mature protein sequence was cloned into the pET23a vector and expressed in Escherichia coli BL21(DE3)pLysS. Recombinant DyP was obtained in high yield as inclusion bodies, and different parameters for its in vitro activation were optimized with a refolding yield of ∼8.5% of the E. coli-expressed DyP. Then, a single chromatographic step allowed the recovery of 17% of the refolded DyP as pure enzyme (1.5mg per liter of culture). The thermal stabilities of wild DyP from A. auricula-judae and recombinant DyP from E. coli expression were similar up to 60°C, but the former was more stable in the 62-70°C range. Stabilities against pH and H2O2 were also measured, and a remarkably high stability at extreme pH values (from pH 2 to 12) was observed. The kinetic constants of recombinant DyP for the oxidation of different substrates were determined and, when compared with those of wild DyP, no important differences were ascertained. Both enzymes showed high affinity for Reactive Blue 19 (anthraquinone dye), Reactive Black 5 (azo dye), 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) and 2,6-dimethoxyphenol, with similar acidic pH optima and oxidative stabilities. Oxidation of veratryl alcohol and a nonphenolic lignin model dimer were confirmed, although as minor enzymatic activities. Interestingly, two sets of kinetic constants could be obtained for the oxidation of Reactive Blue 19 and other substrates, suggesting the existence of more than one oxidation site in this new peroxidase family.