Ultrastructural and Immunocytochemical Studies on the H2O2-Producing Enzyme Pyranose Oxidase in Phanerochaete chrysosporium Grown under Liquid Culture Conditions

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The ultrastructural distribution of the sugar-oxidizing enzyme pyranose 2-oxidase (POD) in hyphae of Phanerochaete chrysosporium K-3 grown under liquid culture conditions optimal for the enzyme's production was studied by transmission electron microscopy immunocytochemistry. Using the 3-dimethylaminobenzoic acid-3-methyl-2-benzothiazolinone hydrazone hydrochloride H2O2 peroxidase spectrophotometric assay, POD was detected in mycelial extracts from days 7 to 18, with maximum activity recorded on day 12. Onset of POD activity occurred in the secondary phase of hyphal development at a time of stationary growth, glucose limitation, and pH increase. POD was also detected extracellularly in the culture fluid from days 7 to 18, with maximum activity recorded on day 13. At early stages of development (3 to 4 days), using anti-POD antibodies and immunogold labeling, POD was localized in multivesicular and electron-dense bodies and in cell membrane regions. After 10 to 12 days of growth, at maximum POD activity, POD was concentrated within the periplasmic space where it was associated with membrane-bound vesicles and other membrane structures. At later stages of development (17 to 18 days), when the majority of hyphae were lysed, POD was observed associated with residual intracellular membrane systems and vesicles. Transmission electron microscopy immunocytochemical studies also demonstrated an extracellular distribution of the enzyme at the stationary growth phase, showing its association with fungal extracellular slime. In studies of ligninolytic cultures of the same fungus, POD was found to have a similar intracellular and extracellular distribution in slime as that recorded for cultures grown with cornsteep. POD's peripheral cytoplasmic distribution shows similarities to the cellular distribution of that reported previously for H2O2-dependent lignin and manganese peroxidases in P. chrysosporium.

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