[1][2] Members of this family have a duplicated structure and generally possess two distinct inhibitory sites.

These inhibitors are primarily found in plants and in particular in the seeds of legumes, as well as in cereal grains.

[4] Proteins of the Bowman–Birk inhibitor family of serine proteinase inhibitors interact with the enzymes they inhibit via an exposed surface loop that adopts the canonical proteinase inhibitory conformation.

This inhibition mechanism is common for the majority of serine proteinase inhibitor proteins, and many analogous examples are known.

A particular feature of the Bowman–Birk inhibitor protein, however, is that the interacting loop is a particularly well-defined, disulfide-linked, short beta-sheet region.