Kinetics of native and modified Bowman-Birk soya-bean trypsin inhibitor on growth and enzymes activities of the chick pancreas

Induction of early response genes in trypsin inhibitor-induced pancreatic growth

Endogenous CCK release induced by a synthetic trypsin inhibitor, camostat, stimulates pancreatic growth; however, the mechanisms mediating this growth are not well established. Early response genes often couple short-term signals with long-term responses. To study their participation in the pancreatic growth response, mice were fasted for 18 h and refed chow containing 0.1% camostat for 1-24 h. Expression of 18 early response genes were evaluated by quantitative PCR; mRNA for 17 of the 18 increased at 1, 2, 4, or 8 h. Protein expression for c-jun, c-fos, ATF-3, Egr-1, and JunB peaked at 2 h. Nuclear localization was confirmed by immunohistochemistry of c-fos, c-jun, and Egr-1. Refeeding regular chow induced only a small increase of c-jun and none in c-fos expression. JNKs and ERKs were activated 1 h after camostat feeding as was the phosphorylation of c-jun and ATF-2. AP-1 DNA binding evaluated by EMSA showed a significant increase 1-2 h after camostat feeding with participation of c-jun, c-fos, ATF-2, ATF-3, and JunB shown by supershift. The CCK antagonist IQM-95,333 blocked camostat feeding-induced c-jun and c-fos expression by 67 and 84%, respectively, and AP-1 DNA binding was also inhibited. In CCK-deficient mice, the maximal response of c-jun induction and AP-1 DNA binding were reduced by 64 and 70%, respectively. These results indicate that camostat feeding induces a spectrum of early response gene expression and AP-1 DNA binding and that these effects are mainly CCK dependent.

Relevance of multiple soybean trypsin inhibitor forms to nutritional quality

Trypsin inhibitors contribute to the antinutritional component of raw soybean meal by inhibiting vertebrate pancreatic serine proteinases in the small intestine, resulting in a range of deleterious physiological effects in the animal. The variation in the nutritional quality of soybean cultivars stems partly from wide-ranging levels of trypsin inhibitor, and from varying proportions of trypsin inhibitors of two classes--the Kunitz and the Bowman-Birk inhibitor classes. The latter class is better able to survive heat processing and digestion in the stomach. Some variation in cultivars also arises from the array of isoinhibitors present in the seed. The three Kunitz isoinhibitors, Ti(a), Ti(b) and Ti(c) differ by as much as 1000-fold in their interaction with bovine trypsin. The Bowman-Birk isoinhibitors differ not only in their extent of interaction with trypsin, but in their spectrum of inhibition of the other pancreatic enzymes, chymotrypsin and elastase. In this chapter, we look at twenty-two Bowman-Birk inhibitors from ten soybean cultivars and find at least twelve which are different enough in amino acid composition and/or inhibitor activity to be distinct protein species. Of these, three pairs are related by proteolytic digestion. Quite ironically, the Bowman-Birk inhibitors, and to some extent the Kunitz inhibitors, contribute to the nutritional quality of soybeans by virtue of their high cystine content which supplements the low or negligible amounts of sulfur-containing amino acids in the storage proteins that comprise the bulk of the protein reserve in the seed.

The Bowman-Birk inhibitor. Trypsin- and chymotrypsin-inhibitor from soybeans

Four decades of studies on the isolation, characterization, properties, structure, function and possible uses of the Bowman-Birk trypsin- and chymotrypsin-inhibitor from soybeans are reviewed. Starting from Bowman's Acetone Insoluble factor, designated Ai, AA and SBTIAA, the Bowman-Birk inhibitor (BBI) was found to be a protein molecule consisting of a chain of 71 amino acids cross linked by 7 disulfide bonds, with a tendency to self-associate. BBI possesses two independent sites of inhibition, one at Lys 16-Ser 17 against trypsin and the other at Leu 43-Ser 44 against chymotrypsin. It forms a 1:1 complex with either trypsin or chymotrypsin and a ternary complex with both enzymes. Ingestion of BBI by rats, chicks or quails affects the size and protein biosynthesis of the pancreas. Establishment of the full covalent structure of BBI revealed a high homology in the sequences around the two inhibitory sites, suggesting evolutionary gene duplication from a single-headed ancestral inhibitor. Scission of BBI by CNBr followed by pepsin results in two active fragments, one that inhibits trypsin and the other, chymotrypsin. Replacements and substitutions in the reactive sites result in changes in inhibitory activity and in specificity of inhibition. Conformation studies, labeling of BBI with a photoreactive reagent, chemical synthesis of cyclic peptides that include inhibitory sites, in vitro synthesis of BBI, and species specificity regarding the inhibited enzymes are described. The significance of BBI as a prototype of a family of inhibitors present in all legume seeds is discussed.