title: Purification and characterization of laccase from Chaetomium thermophilium and its role in humification.
abstract: Chaetomium thermophilium was isolated from composting municipal solid waste during the thermophilic stage of the process. C. thermophilium, a cellulolytic fungus, exhibited laccase activity when it was grown at 45 degreesC both in solid media and in liquid media. Laccase activity reached a peak after 24 h in liquid shake culture. Laccase was purified by ultrafiltration, anion-exchange chromatography, and affinity chromatography. The purified enzyme was identified as a glycoprotein with a molecular mass of 77 kDa and an isoelectric point of 5.1. The laccase was stable for 1 h at 70 degreesC and had half-lives of 24 and 12 h at 40 and 50 degreesC, respectively. The enzyme was stable at pH 5 to 10, and the optimum pH for enzyme activity was 6. The purified laccase efficiently catalyzed a wide range of phenolic substrates but not tyrosine. The highest levels of affinity were the levels of affinity to syringaldazine and hydroxyquinone. The UV-visible light spectrum of the purified laccase had a peak at 604 nm (i.e., Cu type I), and the activity was strongly inhibited by Cu-chelating agents. When the hydrophobic acid fraction (the humic fraction of the water-soluble organic matter obtained from municipal solid waste compost) was added to a reaction assay mixture containing laccase and guaiacol, polymerization took place and a soluble polymer was formed. C. thermophilium laccase, which is produced during the thermophilic stage of composting, can remain active for a long period of time at high temperatures and alkaline pH values, and we suggest that this enzyme is involved in the humification process during composting.
authors.affiliation: Department of Soil and Water Sciences, Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, Rehovot 76100, Israel.
authors.forename: B
authors.initials: B
authors.lastname: Chefetz
authors.forename: Y
authors.initials: Y
authors.lastname: Chen
authors.forename: Y
authors.initials: Y
authors.lastname: Hadar
mesh_terms: D001673:Biodegradation, Environmental; D002597:Chaetomium / Q000201:enzymology* / Q000254:growth & development / Q000302:isolation & purification; D003470:Culture Media; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004795:Enzyme Stability; D006812:Humic Substances / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D042845:Laccase; D010088:Oxidoreductases / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism*; D011108:Polymers / Q000378:metabolism; D013379:Substrate Specificity; D013696:Temperature
chemical_list: D003470:Culture Media; D004791:Enzyme Inhibitors; D006812:Humic Substances; D011108:Polymers; D010088:Oxidoreductases; D042845:Laccase