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PubMed1978

Induction of laccase in Basidiomycetes: apparent activity of the inducible and constitutive forms of the enzyme with phenolic substrates.

The purified preparations of the inducible and constitutive forms of laccase (EC 1.14.18.1) have been obtained from mycelia of Trametes versicolor, Pleurotus ostreatus and Pholiota mutabilis. The activities of the inducible forms of laccase with ferulic acid and other phenolic hydrogen donors were found to be several-fold higher as compared with the constitutive forms.

Basidiomycota↗

PubMed1975

Properties of the glycoprotein laccase immobilized by two methods.

Laccase (p-diphenol:oxygen oxidoreductase; EC 1.10.3.2) from Neurospora crassa has been immobilized by two different procedures: (1) Covalent attachment to Sepharose 4B activated with cyanogen bromide, and (2) Adsorption to Concanavalin A-Sepharose via the carbohydrate moiety. Except for small changes in the Michaelis-Menten constants, no differences were noted in the enzymological properties of the immobilized enzymes when compared to free enzyme. The carbohydrate moiety of laccase involved in the interaction with Concanavalin A does not appear to be closely associated with the active center since binding to the lectin has no effect on the enzymological parameters investigated.

Catechol Oxidase↗

PubMed1976

Kinetic studies of Rhus vernicifera laccase. Evidence for multi-electron transfer and an oxygen intermediate in the reoxidation reaction.

1. The reoxidation of reduced Rhus vernicifera laccase (monophenol,dihydroxyphenylalanine:oxygen oxidoreductase, EC 1.14.18.1) by molecular oxygen has been studied by optical absorption and EPR methods. 2. The reoxidation by oxygen of the type 1 Cu+ and the two-electron acceptor is characterized by a second-order rate constant of about 5-10(6) M-1-s-1. 3. The appearance of an optical intermediate (with an absorbance maximum around 360 nm) parallels the reoxidation of type 1 Cu+ and the two-electron acceptor. It disappears in a first-order reaction with a half-time of 20 s. A similar intermediate is formed during normal turnover. 4. The type 2 Cu+ appears to be reoxidized in an intramolecular reaction with a half-time of about 20 s, suggesting a correlation between the reoxidation of this site and the disappearance of the optical intermediate. 5. The results suggest that three electrons are rapidly transferred to oxygen leading to the formation of an enzyme-bound oxygen intermediate.

Catechol Oxidase↗

PubMed1975

EPR studies on the anaerobic reduction of fungal laccase. Evidence for participation of type 2 copper in the reduction mechanism.

1. In anaerobic reduction studies on fungal laccase B (p-diphenol:O2 oxidoreductase, EC 1.14.18.1) with the EPR and stopped-flow techniques it was found that the type 2 copper of the enzyme is rapidly undergoing a reduction-oxidation cycle which is followed by a slower reduction in a couple of seconds. An intermediate EPR signal of unknown origin is formed in the same time-range as the initial reduction of type 2 copper and disappears again when this copper ion is reoxidized. 2. The rate of the anaerobic reoxidation of type 2 copper is similar to the reduction rate of the two-electron acceptor, suggesting that they are interacting in the electron transfer of the enzyme. 3. The changes in the reaction rates of both type 2 and type 3 copper appear to be affected in a similar way by changes in pH. 4. The EPR signal of the type 2 Cu2+ suggests that this ion is liganded to one or more nitrogens.

Anaerobiosis↗

PubMed1978

The state of copper in Neurospora laccase.

1. Neurospora crassa laccase has been prepared from the growth medium and studied by optical absorption, circular dichroism and electron paramagnetic resonance (EPR) spectroscopy. The molecular weight, the copper content and the amino acid composition have also been determined. 2. The molecular weight as determined by gel filtration in 6 M guanidine hydrochloride and by sodium dodecyl sulfate gel electrophoresis is found to be 64 000. The enzyme contains 3.8 copper ions per 64 000. 3. The visible and the near ultraviolet difference absorption spectrum shows two maxima, at 330 and 595 nm, and a shoulder at about 720 nm. The circular dichroism spectrum between 300 and 760 nm contains five bands in the oxidized enzyme. After reduction of the enzyme with ascorbate there remains only a band at 305 nm. 4. EPR measurements show that 52% of the total copper in the protein is paramagnetic. Two EPR signals of equal intensity with different hyperfine splitting constants, of 9 and 18.5 mT, are present, which are assigned to Type 1 Cu2+ and Type 2 Cu2+, respectively, as found in other blue copper-containing oxidases.

Amino Acids↗

PubMed1978

Reductant-dependent electron distribution among redox sites of laccase.

Rhus laccase (monophenol monooxygenase, monophenol,dihydroxyphenylalanine:oxygen oxidoreductase, EC 1.14.18.1) an O2/H2O oxidoreductase containing four copper ions bound to three redox sites (type 1, type 2, and type 3 Cu pair), was titrated anaerobically with several reductants having various chemical and thermodynamic properties. The distribution of electron equivalents among the redox sites was found to be reductant dependent. When the data for titration by various reductants of the type 3 site were plotted against those of the type 1 site according to the Nernst formalism, the slope n varied from 2.0 to 1.0. The redox potential of the reductant's first oxidation step is qualitatively correlated with the value of n and is suggested as the factor that modulates the electron distribution. Such a behavior implies a nonequilibrium situation. A very good simulation of the data was provided by an analysis assuming a formally variable cooperativity between the two type 3 copper ions. This apparent variability is suggested to result from a process whereby sufficiently strong reductants induce a transition of the type 3 site from a cooperative two-electron acceptor to a pair of independent one-electron acceptors. This uncoupled state of the type 3 site is considered metastable. Other possible models were also investigated. Summarizing the available data, we conclude that the two-electron accepting behavior of the 330-nm chromophore is the exception rather than the rule.

Anaerobiosis↗

PubMed1979

Asymmetric diphenol formation by a fungal laccase.

A laccase isolated from the fungus Rhizoctonia praticola catalyzed the cross-coupling of two differently halogenated phenols. When 2,4-dichlorophenol and 4-bromo-2-chlorophenol were incubated together with the enzyme, three dimers were formed and isolated by thin-layer chromatography. The molecular weights of these compounds were determined by mass spectrometry as 322, 410, and 366, which correspond with the respective dimers of each of the phenols and with a hybrid formed from both, tentatively assigned the structure 3,3',5'-trichloro-5-bromo-2,2'-diphenol. Gas chromatography-mass spectrometry analysis of these products and of their methylated derivatives lent support to these structural assignments.

Catechol Oxidase↗

PubMed1979

Oxidative and demethylating activity of multiple forms of laccase from Pholiota mutabilis.

1. The inducible and constitutive forms of laccase from the fungus Pholiota mutabilis show both the oxidative and demethylating activity, which proves the bifunctional character of the enzyme. 2. The oxidative/demethylating activity ratio of the forms induced either with ferulic or syringic acid is different from that shown by the constitutive form. 3. Splitting of one methoxyl group from the methoxyphenol substrate is associated with the release of one molecule of methanol.

Agaricales↗

PubMed1976