The Properties of Extracellular Enzymes of Venturia inaequalis and Their Association with Loss of Virulence of the Fungus in Culture

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Abstract
Summary: Ribonuclease, deoxyribonuclease, acid phosphatase and phenoloxidase were detected in preparations of extracellular melanoprotein isolated from cultures of Venturia inaequalis. The high initial levels of activity produced per g fungus declined within a few days of inoculation, to an approximately constant level. About six times as much activity was released by conidia germinating in medium enriched with wood extract than was released in basal medium. After 5 d incubation, the rate of production of enzymically active melanoprotein reflected the rate of growth of the fungus. Isolated melanoprotein stored at 4 °C for 3 months showed up to 190% more hydrolase activity than was measured originally, but longer storage caused a subsequent decrease in activity. Only phenoloxidase decreased continuously during storage. The apparent stability of the bond between melanin and protein under dissociating conditions contrasted with the reversible formation of complexes between the fungal product and polyelectrolytes.