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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. A set of re-isolates of different ages produced randomly variable levels of hydrolase activity when cultured repeatedly over a period of 16 months. On each occasion, however, the specific and total activity of each hydrolase was (with one marginal exception) lower in cultures of the oldest re-isolate than in those of the later re-isolates. In contrast, the specific activity of phenoloxidase was highest in cultures of the oldest re-isolate. These changes were associated with the decline in virulence observed in stored re-isolates of clone E1 of V. inaequalis. |
