"Decolorization and Kinetics of Reactive Dyes by Native Laccases from Northeast Mexico"-Edición Única

Abstract

Laccase isoforms Lac-I and Lac-II produced by the basidiomicete Pycnoporus sanguineus were investigated. Both enzymes presented high stability during prolonged storage under freezing conditions (-20 o C) with no significant activity reduction. For RBBR, decolorization efficiencies range from 82 to 88% after 3 hours of incubation for both isoforms at 1 and 8 U mL-1 . However, with 8 U mL-1 the decolorization ranges between 70 to 80% during the first 5 minutes of incubation. A significant lower decolorization pattern was observed with RB-5 reaching a maximum decolorization efficiency of 50% after 15 hr of incubation. For this time, the enzymatic decolorization of RB-5 with 1 U mL -1 was between 14 to 27% and at the high laccase activity level, 8 U mL-1 , was from 33 to 53%. The use of laccase mediators was applied to improve RB-5 decolorization rates using violuric acid and N-hydroxypthalamide. Violuric acid reduced decolorization time from 15 hr to 25 min with 1 mM and 1 U mL -1 of enzyme activity and reaching up to 80% decolorization. The maximum decolorization efficiency obtained with N-HPT was 71% after 15 hr of incubation. Kinetic parameters of the two laccases were determined using RBBR as substrate: Km was 0.243 and 0.117 mM and Vmax was 1.233 and 1.012 mM sec-1 for Lac-I and Lac-II respectively. Both enzymes have high decolorization power for dye decolorization although Lac-I was slightly more active against RBBR and RB-5 than Lac-II throughout the experimentation. These enzymes demonstrated high potential against both dyes and have significant differences in comparison to other reported enzymes.