The soybean trypsin inhibitor (Kunitz) family [1] is one of the numerous families of proteinase inhibitors. It comprise plant proteins which have inhibitory activity against serine proteinases from the trypsin and subtilisin families, thiol proteinases and aspartic proteinases as well as some proteins that are probably involved in seed storage. This family is currently known to group the following proteins:

• Trypsin inhibitors A, B, C, KTI1, and KTI2 from soybean.
• Trypsin inhibitor DE3 from coral beans (Erythrina sp.).
• Trypsin inhibitor DE5 from sandal bead tree.
• Trypsin inhibitors 1A (WTI-1A), 1B (WTI-1B), and 2 (WTI-2) from goa bean.
• Trypsin inhibitor from Acacia confusa.
• Trypsin inhibitor from silk tree.
• Chymotrypsin inhibitor 3 (WCI-3) from goa bean.
• Cathepsin D inhibitors PDI and NDI from potato [2], which inhibit both cathepsin D (aspartic proteinase) and trypsin.
• α-amylase/subtilisin inhibitors from barley and wheat.
• Albumin-1 (WBA-1) from goa bean seeds [3].
• Miraculin from Richadella dulcifica [4], a sweet taste protein.
• Sporamin from sweet potato [5], the major tuberous root protein.
• Thiol proteinase inhibitor PCPI 8.3 (P340) from potato tuber [6].
• Wound responsive protein gwin3 from poplar tree [7].
• 21 Kd seed protein from cocoa [8].

All these proteins contain from 170 to 200 amino acid residues and one or two intrachain disulfide bonds. The best conserved region is found in their N-terminal section and is used as a signature pattern.