ABSTRACT
Properties of cellobiose:quinone oxidoreductase (CBQ), cellobiose dehydrogenase (CDH), glyoxal oxidase (GLOX), glucose oxidases and veratryl alcohol oxidase (VAO) are reviewed. There is strong evidence that CDH reduces quinones, phenoxy and cation radicals. Glucose oxidases (glucose 1-oxidase and pyranose 2-oxidase) and VAO have been less investigated but evidence for reduction of the above compounds is accumulating. Pyranose oxidase, glyoxal oxidase and VAO are very important for hydrogen peroxide production by white-rot fungi. CDH is only produced on cellulose or on wood, whereas pyranose oxidase and VAO are produced both on wood and on rich glucose media suggesting that the lignin degrading white-rot fungi may use different quinone and radical reducing enzymes to regulate lignin polymerization/depolymerization depending on the substrate and cultivation conditions. Intracellular quinone reductases are also produced. Whether brown-rot fungi in general produce CBQ/CDH or VAO is not clear. The Fe(III) reducing ability of both CDH and certain phenolate compounds agree with the rapid depolymerization of cellulose by brown-rot fungi. The interaction of Fe(III) reduction with the hydrogen peroxide producing system in white-rot and brown-rot fungi requires more investigation.
Subject(s)
Alcohol Oxidoreductases/metabolism , Carbohydrate Dehydrogenases/metabolism , Fungi/enzymology , Lignin/metabolism , Iron/metabolism , Peroxidases , Quinones/metabolismABSTRACT
This method was proposed earlier for measuring glucose in a peroxidase-glucose oxidase system but has not been studied for determination of manganese peroxidase (MnP) activity. The assay is based on the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone (MBTH) and 3-(dimethylamino)benzoic acid (DMAB). The reaction of MBTH and DMAB in the presence of H2O2, Mn2+, and MnP gives a deep purple-blue color with a broad absorption band with a peak at 590 nm. The extinction coefficient is high (53,000 M-1 cm-1), so low MnP activities can be detected. Lignin peroxidase and laccase, usually present in cultures of white rot fungi, gave little or no interference at the concentrations tested. However, slight interference from very high LiP activity may occur at very low MnP activity.
Subject(s)
Aminobenzoates/metabolism , Peroxidases/metabolism , Thiazoles/metabolism , Benzothiazoles , Calibration , Hydrazones , Hydrogen Peroxide , Kinetics , Manganese , Oxidation-Reduction , Spectrophotometry , Substrate Specificity , meta-AminobenzoatesABSTRACT
Reduction of H2O2-oxidized manganese peroxidase (MnP), lignin peroxidase and, to some extent, horseradish peroxidase, was studied in the presence of cellobiose oxidase (CbO) and cellobiose. It was found that the reversion rates for MnP compound II and lignin peroxidase compound II back to native enzymes increased significantly in the presence of CbO and cellobiose. However, the reduction of cytochrome c by CbO plus cellobiose was 40 times faster than the reduction of MnP compound II. Also, the lag phase before reversion to the native states decreased for all three peroxidases in the presence of CbO and cellobiose. Active CbO did not repress formation of compounds I or II of the peroxidases, and Mn2+/veratryl alcohol reduced compound II of the peroxidases much more rapidly than did active CbO. This indicates that, in the presence of Mn2+ or veratryl alcohol, MnP and lignin peroxidase can complete their catalytic cycles and function normally without interference from CbO. Without the presence of peroxidase substrates, active CbO reduced compound II of the above peroxidases.