Soy‐ghretropin, a novel ghrelin‐releasing peptide derived from soy protein

We investigated exogenous secretagogues of ghrelin, which is an orexigenic hormone isolated from the stomach. We found that the tryptic digest of soy β-conglycinin stimulated ghrelin secretion by the ghrelin-producing cell line, MGN3-1. We then identified a 22-amino acid peptide corresponding to the β-conglycinin α-subunit(192–213) [βCGα(192–213)] from an active fraction separated by HPLC. The N-terminal undecapeptide of βCGα(192–213), NKNPFLFGSNR, exhibited ghrelin-releasing activity at a lower dose than that of βCGα(192–213). We named NKNPFLFGSNR ‘soy-ghretropin’, which corresponds to βCGα(192–202). Neither [des-N1K2]-soy-ghretropin nor [des-R11]-soy-ghretropin stimulated ghrelin secretion; hence, both the N- and C-terminal structures of soy-ghretropin were indispensable. Orally administered soy-ghretropin increased plasma ghrelin levels and food intake in vivo. Soy-ghretropin is the first exogenous ghrelin-releasing peptide derived from food protein.