This study was an attempt to explain the variability of in vivo sensitivity of wood decay fungi to the chitin synthetase (CS) inhibitor, polyoxin, by comparing CS distribution in cellular fractions. The five species studied were the brown-rot fungi Coniophora puteana, Gloeophyllum trabeum, Fibuloporia vaillantii, and the white-rot fungi Schizophyllum commune and Ganoderma applanatum. The CS activity was measured in crude homogenates of disrupted mycelia and centrifugation fractions consisting of 10,000 x g precipitate (cell wall fraction), 45,000 x g precipitate (mixed membrane fraction), and 45,000 x g supernatant (cytosol). Enzyme activity was different in all fractions of the same species and in the same fractions of the different species. There was great variation in CS activity of cellular fractions of the five species. The highest activity was in the cell wall and mixed membrane fractions of Schizophyllum commune, the species previously shown to have the highest in vivo polyoxin sensitivity. Trypsin increased the CS activity in cytosol of Ganoderma applanatum, but not in digitonin-treated cell wall or membrane fractions. Variability of fungal response to polyoxin D appears to be related to cellular location and activity of CS.

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