The effect of lignin model compound structure on the rate of oxidation catalyzed by two different fungal laccases

Maarit Lahtinen (Corresponding Author), Kristiina Kruus, Harry Boer, Marianna Kemell, Martina Andberg, Liisa Viikari, Jussi Sipilä

Research output: Contribution to journalArticleScientificpeer-review

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Abstract

Laccases (EC 1.10.3.2) are multicopper oxidases able to oxidize various substrates, such as phenolic subunits of lignin. The substrate range can be widened to non-phenolic units by the use of mediators. Since discovery of the laccase-mediator system, direct reactions of lignin and laccase without mediated electron-transfer have gained much less attention. The objective of this study was to investigate lignin as a substrate for fungal laccases by using lignin model compounds. These model compounds contained guaiacylic and syringylic moieties and also compounds of guaiacylic origin at a higher oxidation level. Some of these compounds are commercially available, but most of them were synthesized. The oxidation reaction rates of the lignin model compounds were studied by monitoring consumption of the co-substrate oxygen, in reactions catalyzed by laccases from two different fungi; Melanocarpus albomyces and Trametes hirsuta, possessing different molecular and catalytic properties. These reaction rate studies were compared to physicochemical properties of the lignin model compounds: relative redox potentials determined using cyclic voltammetry and pKa-values. Docking of syringylic and biphenylic compounds to the active sites of both laccases was performed and the resulting model complex structures were used to further interpret the reaction rate results. Reaction rates of laccases are mainly affected by the ability of a lignin model compound to be oxidized and the pKa-value of the substrate seems to be less important. As a consequence, syringylic compounds are oxidized with the highest rates and compounds at a higher oxidation level and redox-potential, such as vanillin, are oxidized at a much lower rate. Both guaiacylic and syringylic type compounds fit well in the active sites of both laccases. Only for a biphenylic compound, steric clashes were observed, and they are likely to have an effect on the reaction rate. When the oxidation rates on the selected model compounds with the two different laccases were compared, the redox-potential difference between laccases T1 copper and the lignin model compound (ΔE) was not the only property that determined the oxidation rate. In the case of lignin model substrates, also the selectivity of a specific laccase, reflected in the kcat/Km value, plays an important role.
Original languageEnglish
Pages (from-to)204-210
Number of pages7
JournalJournal of Molecular Catalysis B: Enzymatic
Volume57
Issue number1-4
DOIs
Publication statusPublished - 2009
MoE publication typeA1 Journal article-refereed

Fingerprint

Laccase
Lignin
Oxidation
Reaction rates
Substrates
Oxidation-Reduction
Catalytic Domain
Trametes
Fungi
Cyclic voltammetry
Copper
Oxidoreductases
Oxygen
Electrons
Monitoring

Keywords

  • Laccase
  • lignin
  • oxidation
  • cyclic voltammetry
  • docking

Cite this

Lahtinen, Maarit ; Kruus, Kristiina ; Boer, Harry ; Kemell, Marianna ; Andberg, Martina ; Viikari, Liisa ; Sipilä, Jussi. / The effect of lignin model compound structure on the rate of oxidation catalyzed by two different fungal laccases. In: Journal of Molecular Catalysis B: Enzymatic. 2009 ; Vol. 57, No. 1-4. pp. 204-210.
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The effect of lignin model compound structure on the rate of oxidation catalyzed by two different fungal laccases. / Lahtinen, Maarit (Corresponding Author); Kruus, Kristiina; Boer, Harry; Kemell, Marianna; Andberg, Martina; Viikari, Liisa; Sipilä, Jussi.

In: Journal of Molecular Catalysis B: Enzymatic, Vol. 57, No. 1-4, 2009, p. 204-210.

Research output: Contribution to journalArticleScientificpeer-review

TY - JOUR

T1 - The effect of lignin model compound structure on the rate of oxidation catalyzed by two different fungal laccases

AU - Lahtinen, Maarit

AU - Kruus, Kristiina

AU - Boer, Harry

AU - Kemell, Marianna

AU - Andberg, Martina

AU - Viikari, Liisa

AU - Sipilä, Jussi

PY - 2009

Y1 - 2009

N2 - Laccases (EC 1.10.3.2) are multicopper oxidases able to oxidize various substrates, such as phenolic subunits of lignin. The substrate range can be widened to non-phenolic units by the use of mediators. Since discovery of the laccase-mediator system, direct reactions of lignin and laccase without mediated electron-transfer have gained much less attention. The objective of this study was to investigate lignin as a substrate for fungal laccases by using lignin model compounds. These model compounds contained guaiacylic and syringylic moieties and also compounds of guaiacylic origin at a higher oxidation level. Some of these compounds are commercially available, but most of them were synthesized. The oxidation reaction rates of the lignin model compounds were studied by monitoring consumption of the co-substrate oxygen, in reactions catalyzed by laccases from two different fungi; Melanocarpus albomyces and Trametes hirsuta, possessing different molecular and catalytic properties. These reaction rate studies were compared to physicochemical properties of the lignin model compounds: relative redox potentials determined using cyclic voltammetry and pKa-values. Docking of syringylic and biphenylic compounds to the active sites of both laccases was performed and the resulting model complex structures were used to further interpret the reaction rate results. Reaction rates of laccases are mainly affected by the ability of a lignin model compound to be oxidized and the pKa-value of the substrate seems to be less important. As a consequence, syringylic compounds are oxidized with the highest rates and compounds at a higher oxidation level and redox-potential, such as vanillin, are oxidized at a much lower rate. Both guaiacylic and syringylic type compounds fit well in the active sites of both laccases. Only for a biphenylic compound, steric clashes were observed, and they are likely to have an effect on the reaction rate. When the oxidation rates on the selected model compounds with the two different laccases were compared, the redox-potential difference between laccases T1 copper and the lignin model compound (ΔE) was not the only property that determined the oxidation rate. In the case of lignin model substrates, also the selectivity of a specific laccase, reflected in the kcat/Km value, plays an important role.

AB - Laccases (EC 1.10.3.2) are multicopper oxidases able to oxidize various substrates, such as phenolic subunits of lignin. The substrate range can be widened to non-phenolic units by the use of mediators. Since discovery of the laccase-mediator system, direct reactions of lignin and laccase without mediated electron-transfer have gained much less attention. The objective of this study was to investigate lignin as a substrate for fungal laccases by using lignin model compounds. These model compounds contained guaiacylic and syringylic moieties and also compounds of guaiacylic origin at a higher oxidation level. Some of these compounds are commercially available, but most of them were synthesized. The oxidation reaction rates of the lignin model compounds were studied by monitoring consumption of the co-substrate oxygen, in reactions catalyzed by laccases from two different fungi; Melanocarpus albomyces and Trametes hirsuta, possessing different molecular and catalytic properties. These reaction rate studies were compared to physicochemical properties of the lignin model compounds: relative redox potentials determined using cyclic voltammetry and pKa-values. Docking of syringylic and biphenylic compounds to the active sites of both laccases was performed and the resulting model complex structures were used to further interpret the reaction rate results. Reaction rates of laccases are mainly affected by the ability of a lignin model compound to be oxidized and the pKa-value of the substrate seems to be less important. As a consequence, syringylic compounds are oxidized with the highest rates and compounds at a higher oxidation level and redox-potential, such as vanillin, are oxidized at a much lower rate. Both guaiacylic and syringylic type compounds fit well in the active sites of both laccases. Only for a biphenylic compound, steric clashes were observed, and they are likely to have an effect on the reaction rate. When the oxidation rates on the selected model compounds with the two different laccases were compared, the redox-potential difference between laccases T1 copper and the lignin model compound (ΔE) was not the only property that determined the oxidation rate. In the case of lignin model substrates, also the selectivity of a specific laccase, reflected in the kcat/Km value, plays an important role.

KW - Laccase

KW - lignin

KW - oxidation

KW - cyclic voltammetry

KW - docking

U2 - 10.1016/j.molcatb.2008.09.004

DO - 10.1016/j.molcatb.2008.09.004

M3 - Article

VL - 57

SP - 204

EP - 210

JO - Journal of Molecular Catalysis B: Enzymatic

JF - Journal of Molecular Catalysis B: Enzymatic

SN - 1381-1177

IS - 1-4

ER -