[An inhibitor of enteropeptidases and trypsin from the bovine duodenum]

Enteropeptidase inhibitor (DI) was isolated from bovine duodenum during purification of this enzyme. DI was purified by affinity chromatography on immobilised trypsin. DI preparations contain two main components: DI-9 (9 kD) and DI-20 (20 kD). The N-terminal amino acid sequence 1-19 of DI-9 is highly homologous to the Kunitz inhibitor (BPI). Molecular weights of DI-9 and BPI are the same (gel electrophoresis data). Fragment 1-19 of DI-9 differs from the corresponding region of BPI only at the position 17: DI-9 contains Ala-17 instead of Arg in BPI. The homology of N-terminal amino acid sequence 1-25 of DI-20 with the corresponding regions of some phospholipases A2 suggests that this protein is a new intestinal phospholipase A2. Inhibitor DI-9 and phospholipase DI-20 are probably isolated in a common lipoprotein complex. The only earlier known in vitro inhibitor of enteropeptidase, BPI, was localised in vivo in different tissues with this enzyme. In our opinion the Kunitz-type inhibitor DI-9 is, a physiological inhibitor of enteropeptidase.