Full-length and N-terminally truncated chicken intestinal diazepam- binding inhibitor. Purification, structural characterization and influence on insulin release

Two forms of diazepam-binding inhibitor (DBI) have been purified from chicken intestine and identified as the intact avian polypeptide (residues 1- 86) and a truncated variant (residues 35-86). At 10 nM concentration, both the intact and the truncated peptide suppress in vitro-monitored glucose induced insulin release by 50 (p <0.02) and 64% (p <0.01), respectively. The truncation starts at a segment, -Thr-Val-Gly-Asp-, that is strictly conserved between characterized DBI species, indicating special restrictions on the structure. However, overall DBI conservation appears to be complex. A number of differently bioactive fragments with separate processings and tissue distributions have been observed, suggesting multiple functions of DBI and its sub-segments.