Product profiles in enzymic and non-enzymic oxidations of the lignin model compound erythro-1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol

Lignin-degrading peroxidases from genome of selective ligninolytic fungus Ceriporiopsis subvermispora

The white-rot fungus Ceriporiopsis subvermispora delignifies lignocellulose with high selectivity, but until now it has appeared to lack the specialized peroxidases, termed lignin peroxidases (LiPs) and versatile peroxidases (VPs), that are generally thought important for ligninolysis. We screened the recently sequenced C. subvermispora genome for genes that encode peroxidases with a potential ligninolytic role. A total of 26 peroxidase genes was apparent after a structural-functional classification based on homology modeling and a search for diagnostic catalytic amino acid residues. In addition to revealing the presence of nine heme-thiolate peroxidase superfamily members and the unexpected absence of the dye-decolorizing peroxidase superfamily, the search showed that the C. subvermispora genome encodes 16 class II enzymes in the plant-fungal-bacterial peroxidase superfamily, where LiPs and VPs are classified. The 16 encoded enzymes include 13 putative manganese peroxidases and one generic peroxidase but most notably two peroxidases containing the catalytic tryptophan characteristic of LiPs and VPs. We expressed these two enzymes in Escherichia coli and determined their substrate specificities on typical LiP/VP substrates, including nonphenolic lignin model monomers and dimers, as well as synthetic lignin. The results show that the two newly discovered C. subvermispora peroxidases are functionally competent LiPs and also suggest that they are phylogenetically and catalytically intermediate between classical LiPs and VPs. These results offer new insight into selective lignin degradation by C. subvermispora.

DyP-like peroxidases of the jelly fungus Auricularia auricula-judae oxidize nonphenolic lignin model compounds and high-redox potential dyes

The jelly fungus Auricularia auricula-judae produced an enzyme with manganese-independent peroxidase activity during growth on beech wood (approximately 300 U l(-1)). The same enzymatic activity was detected and produced at larger scale in agitated cultures comprising of liquid, plant-based media (e.g. tomato juice suspensions) at levels up to 8,000 U l(-1). Two pure peroxidase forms (A. auricula-judae peroxidase (AjP I and AjP II) could be obtained from respective culture liquids by three chromatographic steps. Spectroscopic and electrophoretic analyses of the purified proteins revealed their heme and peroxidase nature. The N-terminal amino acid sequence of AjP matched well with sequences of fungal enzymes known as "dye-decolorizing peroxidases". Homology was found to the N-termini of peroxidases from Marasmius scorodonius (up to 86%), Thanatephorus cucumeris (60%), and Termitomyces albuminosus (60%). Both enzyme forms catalyzed not only the conversion of typical peroxidase substrates such as 2,6-dimethoxyphenol and 2,2'-azino-bis(3-ethylthiazoline-6-sulfonate) but also the decolorization of the high-redox potential dyes Reactive Blue 5 and Reactive Black 5, whereas manganese(II) ions (Mn(2+)) were not oxidized. Most remarkable, however, is the finding that both AjPs oxidized nonphenolic lignin model compounds (veratryl alcohol; adlerol, a nonphenolic beta-O-4 lignin model dimer) at low pH (maximum activity at pH 1.4), which indicates a certain ligninolytic activity of dye-decolorizing peroxidases.

Biotransformation of myrislignan by rat liver microsomes in vitro

Myrislignan (1), erythro-(1R,2S)-2-(4-allyl-2,6-dimethoxyphenoxyl)-1-(4-hydroxy-3-methoxyphenyl) propan-1-ol, is a major acyclic neolignan in seeds of Myristica fragrans. Studies have suggested that myrislignan may deter feeding activity, but little is known about its metabolism. We investigated the biotransformation of myrislignan by rat liver microsomes in vitro. Seven metabolites were produced by liver microsomes from rats pre-treated with sodium phenobarbital. These were identified, using spectroscopic methods, as myrislignanometins A-G (2-8), respectively.