The basidiomycete Marasmius quercophilus is commonly found during autumn on the decaying litter of the evergreen oak (Quercus ilex L.), a plant characteristic of Mediterranean forest. This white-rot fungus colonizes the leaf surface with rhizomorphs, causing a total bleaching of the leaf. In synthetic liquid media, this white-rot fungus has strong laccase activity. From a three-step chromatographic procedure, we purified a major isoform to homogeneity. The gene encodes a monomeric glycoprotein of approximately 63 kDa, with a 3.6 isoelectric point, that contains 12% carbohydrate. Spectroscopic analysis of the purified enzyme (UV/visible and electron paramagnetic resonance, atomic absorption) confirmed that it belongs to the "blue copper oxidase" family. With syringaldazine as the substrate, the enzyme's pH optimum was 4.5, the optimal temperature was 75°C, and the K m was 7.1 M. The structural gene, lac1, was cloned and sequenced. This gene encodes a 517-aminoacid protein 99% identical to a laccase produced by PM1, an unidentified basidiomycete previously isolated from wastewater from a paper factory in Spain. This similarity may be explained by the ecological distribution of the evergreen oak in Mediterranean forest.Litter mineralization is an important component of biogeochemical cycles in terrestrial environments. Lignin is the most difficult litter polymer to degrade, and the only organisms known to completely mineralize lignin are white-rot fungi (6,17). In the last two decades, several such organisms have been studied. At present, three main enzymes (i.e., manganese and lignin peroxidases and laccases) (15, 30) are implicated in the biodegradation of lignin. In addition to fundamental studies on lignin mineralization, these enzymes also have potential uses in industrial processes such as the bleaching of paper pulp (1) or the remediation of xenobiotics in effluents (3). There is no clear relationship between the distribution of ligninolytic enzymes and lignin degradation, since white-rot fungi with only one, with a combination of two, or with all three enzymes are known and can degrade lignin (15,27,34).The role of laccases in lignin degradation has only recently become well established (38). Laccases (p-diphenol oxidase, EC 1.10.3.2) are polyphenol oxidases that catalyze the reduction of oxygen to water with a concomitant oxidation of phenolic compounds. They are typically glycoproteins containing 2 to 4 atoms of copper per molecule and are found in plants and fungi (25,33,35).The evergreen oak (Quercus ilex) forms a characteristic forest climax common in the Western Mediterranean area (22,28). The leaf of Q. ilex, highly lignous and covered by a thick and waxy upper cuticle, is typical of sclerous plants exposed to dryness, particularly during the summer. The white-rot fungus Marasmius quercophilus colonizes dead leaves of Quercus ilex (32). Under favorable temperature and humidity conditions, i.e., in autumn and sometimes in May and June, this fungus becomes predominant among litter fungi and produces ma...

[reaction: see text] The association of lipase-catalyzed enzymatic resolution with in situ racemization mediated with the thiyl radical enables the dynamic kinetic resolution of non-benzylic amines. It leads to (R)-amides with high enantioselectivities. It can be applied either to the conversion of racemic mixtures or to the inversion of (S)-enantiomers.

The racemization of nonactivated aliphatic amines has been mediated with alkanethiols and with methyl thioglycolate in the presence of AIBN. The process involves reversible H-abstraction at the chiral center, in a position alpha relative to nitrogen, by thiyl radical. The knowledge of the reaction enthalpy is critical to select the appropriate thiol. In the absence of experimental values, theoretical calculations of the alpha-C-H BDEs and the S-H BDE provide a useful guide.

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Thiyl radical mediated reversible H abstraction from the stereogenic center α to the nitrogen atom is a mild method to racemize benzylic amines. Owing to the sensitivity of atom‐transfer reactions to enthalpic effects, a knowledge of both the S–H and the α‐C–H bond dissociation energies is fundamental to select the thiol that is appropriate to abstract the hydrogen atom from a given amine. In the absence of experimental data, theoretical calculations supply a useful predictive tool. The experiments described here are helpful in delineating the optimal conditions that have to be fulfilled for the racemization to proceed in a reasonable time in the presence of either a stoichiometric or a catalytic amount of thiol. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)