Inactive proteinases in silkmoth moulting gel

The moulting gel of silkmoths lacks proteolytic activity but contains an inactive form of the proteinases which are later found in the moulting fluid. These inactive enzymes are activatable in vitro by dilution, activation proceeding most rapidly at low ionic strength. Activation proceeds as a first-order process and is not autocatalytic. Approximately the full amount of proteinases ultimately found in moulting fluid are already present in the gel. Moulting gel does not inhibit the active proteinases of moulting fluid; moreover, the proteolytic activity elicited by dilution of the moulting gel does not disappear upon reconcentration. These observations suggest that the proteinases in moulting gel are not inhibited by a stable, dissociable inhibitor; they may be present either as compartmentalized active enzymes or as proenzymes. Several possible mechanisms for the in vivo activation at the time of gel to fluid transformation are discussed.