SUMMARY: The release of proteinase activity from myxamoebae of after suspension in non-nutrient buffer has been confirmed. Between 15% and 30% of the total activity against Hide Powder Azure was released, the bulk of this appearing in the buffer within 30 min. Activity against the cathepsin B substrate, α-benzoyl-D-arginine 2-naphthylamide, was also released. The release of proteinase activity was more rapid than that of other secreted lysosomal enzymes and was insensitive to cyanide. The extracellular proteinases catalysed both limited and extensive proteolysis. Gel electrophoresis showed similar patterns of released and intracellular proteinases, and their sensitivities to inhibitors were also similar. However, there was evidence for an increased proportion of thiol proteinases in the released enzymes. The results suggest that proteinases were released by a non-secretory process but one possible mechanism, cell lysis, has not been clearly demonstrated. A specific developmental role for extracellular proteinases seems unlikely.


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