Comparative Studies on Dehydrogenative Polymerization of Coniferyl Alcohol by Laccases and Peroxidases. Part 1. Preliminary Results

Laccase from Rhus vernicifera Stokes oxidized coniferyl alcohol (1) very slowly in acetone-Water (1 : 1, v/v) in the presence of molecular oxygen. At the reaction time of 144hrs, about 20 mol% of pinoresinol (2), 25 mol % of dehydrodiconiferyl alcohol (3), and 2 mol % of guaiacylglycerol-β-coniferyl ether (4) were produced, but no dehydrogenative polymer (DHP). Laccases from Coriolus versicolor and Pycnoporus coccineus oxidized the substrate faster than Rhus laccase. At the reaction time of 1.5 hrs, Coriolus laccase oxidized the substrate, producing all three dimers and a trace amount of DHP, and Pycnoporus laccase producing dimers 2 and 3 but no DHP. At the reaction time of 12 hrs, Coriolus laccase oxidized the substrate, producing all three dimers and a small amount of DHP, and Pycnoporus laccase producing only DHP but no dimers. Peroxidase type I and II from horseradish (Armoracia rusticana) oxidized the substrate even faster than the laccases in acetone-water (1 :4, v/v) in the presence of hydrogen peroxide, producing DHP predominately at the reaction time of 5 hrs. Tree-laccases may differ from fungal laccases in the oxidation rate and reaction mechanisms. This is probably due to differences in the nature and molecular mass of these glycoproteins, as well as the ligand binding mode of type 2 and type 3 copper sites. During the oxidation by the laccases and peroxidases, the substrate and polymeric products could also undergo biodegradation. The possible role of laccase in biosynthesis of lignin is discussed.