Proteinase inhibitors destined for secretion have an additional N-terminal signal-peptide domain which will be cleaved by a signal-peptidase.

Removal of these one or two N-terminal inhibitor domains, either by interaction with a second peptidase or by autocatalytic cleavage, will activate the zymogen.

[3] Very little is known about the endogenous function of pacifastin-like inhibitors except that they may play roles in arthropod immunity and in regulation of the physiological processes involved in insect reproduction.

Detailed analysis of the 3-D structure shows that these six residues form three disulfide bridges (Cys1–4, Cys2–6, Cys3–5), giving members of the pacifastin family a typical fold and remarkable stability.

The structure of members of this family reveals that they consist of a triple-stranded antiparallel beta-sheet connected by three disulphide bridges.