The Soybean β-Conglycinin β 51–63 Fragment Suppresses Appetite by Stimulating Cholecystokinin Release in Rats

We previously demonstrated that soybean β-conglycinin peptone suppresses food intake and gastric emptying by direct action on rat small intestinal mucosal cells to stimulate cholecystokinin (CCK) release. The aim of the present study was to define the active fragment in β-conglycinin by using synthetic peptides chosen from the sequence of three β-conglycinin subunits. We selected the fragments that had multiple nonadjacent arginine residues, and investigated their ability to bind to components of the rat intestinal brush border membrane as well as to stimulate CCK release and appetite suppression. The fragment from 51 to 63 of the β subunit (β 51–63) had the strongest binding activity. Intraduodenal infusion of β 51–63 inhibited food intake and markedly increased portal CCK concentration. The threshold concentration of β 51–63 to affect food intake was 3 μmol/L. The CCK-A receptor antagonist abolished the β 51–63–induced suppression of food intake. Three types of smaller fragments of β 51–63 (β 51–59, β 53–63 and β 53–59) and two types of fragments similar to β 51–63 in the β-conglycinin α and α′ subunits (α 212–224 and α′ 230–240) had less binding ability than did β 51–63. Model peptides constructed with arginine (R) and glycine (G), such as GRGRGRG, had strong binding affinity, but peptides containing a single R or RR did not. These results indicate that the β-conglycinin β 51–63 fragment is the bioactive appetite suppressant in β-conglycinin, and multiple arginine residues in the fragment may be involved in this effect.