Date

March 1986

Document Type

Dissertation

Degree Name

Ph.D.

Department

Dept. of Biochemistry

Institution

Oregon Graduate Center

Abstract

A correlation was found between lignin degradation and the decolorization of three polymeric dyes (Poly B, Poly R, and Poly Y) by Phanerochaete chrysosporium. Like ligninolytic activity, dye decolorization occurred only during secondary metabolism and was strongly dependent on oxygen concentration. A variety of inhibitors of lignin degradation also inhibited dye decolorization, and a mutant of P. chrysosporium lacking phenol oxidase also was not able to decolorize dyes. In the presence of H2O2 medium from ligninolytic cultures of P. chrysosporium was able to decolorize Poly R and oxidize a variety of lignin model compounds including a diarylpropane and a β-ether dimer. Media from primary growth cultures or a non-ligninolytic mutant had no activity. Chromatography on a blue agarose column revealed that the extracellular media contained two separable peroxidases. One of the enzymes catalyzed the α, β cleavage of diarylpropane. The second enzyme required manganese(II) for activity, and was stimulated by lactate and protein. This manganese-dependent peroxidase was purified to homogeneity by DEAE-sepharose ion-exchange chromatography, blue agarose chromatography, and gel filtration. The peroxidase has an M[subscript r] of 46,000 and contains one molecule of iron protoporphyrin IX. The spectra of the native enzyme and CN[superscript -], N[subscript 3][superscript -] and H2O2 complexes resembled those of horseradish peroxidase. In the presence of Mn(II), NADH and a wide variety of dyes, including Poly B and Poly R were oxidized by the peroxidase. The enzyme rapidly and efficiently oxidises Mn(II) to Mn(III). Manganese(III) was detected and quantified by the characteristic spectra of Mn(III)-pyrophosphate and Mn(III)-lactate complexes. K[subscript m] values for manganese and H2O2 are 80 µM and 140 µM respectively. MnO2was also a product of the enzymatic oxidation of Mn(II). Manganese(III)-lactate was capable of oxidizing NADH and a variety of dyes including Poly B and Poly R. Herein, we propose that the principal function of the Mn-dependent peroxidase is manganese oxidation. The Mn(III) produced by the enzyme in turn oxidizes all the other substrates. The Mn-peroxidase is not present in cultures of P. chrysosporium grown without manganese, but the enzyme rapidly accumulates if Mn(II) is added to the medium. The Mn-peroxidase appears to be the enzyme responsible for the oxidation of Poly R during the first few days of secondary metabolism, but other enzymes probably play a role in dye decolorization in older cultures.

Identifier

doi:10.6083/M4ZP4411

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