This family includes the proteinase B inhibitor from Saccharomyces cerevisiae and the activation peptides from peptidases of the subtilisin family. The subtilisin propeptides are known to function as molecular chaperones, assisting in the folding of the mature peptidase [1], but have also been shown to act as 'temporary inhibitors' [2].

1: Functional analysis of the propeptide of subtilisin E as an intramolecular chaperone for protein folding. Refolding and inhibitory abilities of propeptide mutants. Li Y, Hu Z, Jordan F, Inouye M; J Biol Chem. 1995;270:25127-25132. PMID:7559646

2: The propeptide of subtilisin BPN' as a temporary inhibitor and effect of an amino acid replacement on its inhibitory activity. Kojima S, Minagawa T, Miura K; FEBS Lett. 1997;411:128-132. PMID:9247157