RESUMEN
Proteinase inhibitors are widely distributed in many living organisms and play crucial roles in many biological processes, particularly in regulating the proteinase activity spatially and temporally. However, The Kazal family of serine protease inhibitors is one of the most important and extensively studied protease inhibitor families. This type of protease inhibitor normally consists of one or several domains. Every domain has a highly conserved sequence structure and molecular conformation. It is found that contact residues are hyper variable, which are responsible for the interaction of inhibitors and proteinases. Most of them are in the solvent exposed loop. But P1 residue is the key active site of the interaction between inhibitor and enzyme. The types of the amino acid at P1 site likely play an important role in causing different inhibitory activity. The substitutions at the contact residues cause significant effects on the association constant. By using the Laskowski algorithm, the Ki values of a Kazal domain against six serine proteinases can be predicted from the domain' s sequence alone. At present there are many Kazal proteinase inhibitors found in the organisms, which show important biological functions. This article gives a comprehensive review of the newer developments in the characters and the interaction of the Kazal-type inhibitors.