SECRETION OF AN AMINOPEPTIDASE DURING TRANSITION OF 3RD-STAGE TO 4TH-STAGE LARVAE OF ASCARIS-SUUM

Protease activity was identified in culture fluids collected during in vitro development of L3 to L4 larval stages of Ascaris suum. Fluoroge nic peptide substrates with unblocked N-termini were specifically hydr olyzed indicating aminopeptidase activity; a terminal arginyl residue was preferred, Culture fluids did not hydrolyze fluorogenic peptide su bstrates with blocked N-termini (endopeptidase substrates). The aminop eptidase activity was inhibited by 1,10-phenanthroline (metalloproteas e inhibitor) and by amastatin and bestatin (aminopeptidase inhibitors) ; AEBSF (serine protease inhibitor), Z-pbe-ala-FMK and E-64 (cysteine protease inhibitors), and pepstatin A (aspartyl protease inhibitor) ha d little effect on activity. The apparent molecular weight of the amin opeptidase was estimated gy sucrose density gradient centrifugation at 293 kDa. The aminopeptidase displayed an acidic isoelectric point of 4.7. The peak secretion of the aminopeptidase was temporally associate d with molting and suggests a function for the protease in this comple x process.