Laccase treatment of recycled blue dyed paper: physical properties and fiber charge

Recycled blue colored paper was treated with laccase under various combinations of physical and chemical parameters including enzyme concentration, temperature, oxygen, and reaction time. Laccase treatment of recycled dyed pulp increased acid group content, tear index, tensile index, and color removal in a dose-dependent manner. Lengthening the treatment time from 2 to 4 h was beneficial to acid group content (12% increase), dye removal, and tensile index but had a detrimental 8% decrease on the tear index. A higher reaction temperature (65 vs. 45 degrees C) had a beneficial effect on acid group content (+31%), and tensile index (+26%) and a slightly negative effect on tear index (-5%), but significantly reduced the ability of laccase to remove color. Comparison of reactions subjected to different levels of oxygen supplementation showed the greatest beneficial effect for laccase treatment with slow oxygen bubbling. The experimental results indicate that laccase treatment increases fiber carboxylic acid content and tensile strength, in addition to reducing the color of the enzyme treated paper.     

Use of laccase together with redox mediators to decolourize Remazol Brilliant Blue R

A pure fungal laccase, obtained from a commercial formulation used in the textile industry, did not decolourize Remazol Brilliant Blue R (RBBR). Decolourization was only observed when a small molecular weight redox mediator was added together with the laccase. Under the conditions specified, violuric acid (5.7 mM) was the most effective mediator studied and almost complete decolourization was observed within 20 min. In contrast, 1-hydroxybenzotriazole (HOBT, 11 mM) decolourized RBBR at about a two-fold slower rate and to a lesser extent. Also, higher concentrations of HOBT were inhibitory which could be due to inactivation of laccase by the toxic HOBT radical. The commercial laccase formulation that contained phenothiazine-10-propionic acid as the mediator was least effective, giving 30% decolourization under equivalent conditions. We suggest that similar laccase plus mediator systems could be used for the detoxification of related anthraquinone textile dyes.     

Mechanism of impairment of cytochrome P450-dependent metabolism in hamster liver during leishmaniasis

The mechanism of impairment of cytochrome P450 (P450)-dependent metabolism in hamster liver during leishmaniasis is reported. A significant decrease in the level of P450 was observed on the 20th day of infection when the parasite load in the liver was maximum. The decrease in P450 level was accompanied by a significant increase in the level of marker enzymes of liver and degeneration of liver tissue. The impairment was isozyme-specific and concomitant with the induction of nitric oxide synthase. The results of in vitro experiments with generated nitric oxide and with scavengers demonstrated that the impairment is mediated by NO. Treatment of the infected animals with a combination therapy showed reduction in parasite load, reversal of P450 impairment, and recovery of liver enzymes and tissue close to normal.