HR: 0830h
AN: B21C-0732    [PDF]
TI: Effects of Metal Oxides on a Fungal Laccase Activity and Catechol Transformation
AU: * Ahn, M
EM: mxa35@psu.edu
AF: Laboratory of Soil Biochemistry, The Pennsyvania State University, University Park, PA 16802 United States
AU: Dec, J
EM: jdec@psu.edu
AF: Laboratory of Soil Biochemistry, The Pennsyvania State University, University Park, PA 16802 United States
AU: Bollag, J
EM: jmbollag@psu.edu
AF: Laboratory of Soil Biochemistry, The Pennsyvania State University, University Park, PA 16802 United States
AB: The transformation of naturally occurring phenols to humic polymers is generally catalyzed by various phenoloxidases commonly present in soil. Some poorly crystalline metal oxides and hydroxides may also participate in these reactions. In this study, catechol (0.1 M) was incubated with a fungal laccase (950 unit/mL) in the presence of poorly crystalline minerals (ferrihydrite; 50 mg/mL: birnessite; 1 mg/mL: aluminum hydroxide; 50 mg/mL) to examine the interaction between these soil components under field conditions. Birnessite had an inhibitory effect on the laccase-mediated transformation of catechol (by up to 40%). Enzyme inhibition was possibly caused by the rapid production of humic-like polymers by birnessite. An additional inhibitory effect was caused by Manganese ion released from birnessite as it oxidized catechol (up to 70% loss in enzyme activity). In contrast to birnessite, aluminum hydroxide had an additive effect on the disappearance of catechol despite the rapid adsorption of the enzyme by this mineral (Xm=6.18$\mu$g/mg). Apparently, the adsorbed laccase retained some enzyme activity. Ferrihydrite also had an additive effect on catechol transformation. However, as compared to aluminum hydroxide, ferrihydrite adsorbed less laccase (Xm=0.89$\mu$g/mg) and more humic-like polymers. Unlike birnessite, aluminum hydroxide and ferrihydrite released negligible amounts of metal ions. In conclusion, under field conditions, phenoloxidase activity may be diminished by the presence of birnessite, but the presence of either ferrihydrite or aluminum hydroxide is less likely to inhibit enzyme activity, and may even enhance substrate transformation.
DE: 4807 Chemical speciation and complexation
DE: 4851 Oxidation/reduction reactions
SC: Biogeosciences [B]
MN: 2003 Fall Meeting