Isolation and characterization of oryzatensin: a novel bioactive peptide with ileum-contracting and immunomodulating activities derived from rice albumin.

A novel bioactive peptide was isolated from the tryptic digest of rice soluble protein based on ileum-contracting and anti-opioid activities in the isolated guinea pig ileum. The structure of the peptide was Gly-Tyr-Pro-Met-Tyr-Pro-Leu-Pro-Arg, and it was named oryzatensin. Oryzatensin showed a biphasic ileum-contraction, which was characterized by a rapid contraction followed by a slower one. The latter was mediated by the cholinergic nervous system because it was inhibited by tetrodotoxin and atropine. Although oryzatensin showed weak affinity for mu-opioid receptors, the apparent anti-opioid activity seemed to be associated with the slower contraction. On the other hand, oryzatensin showed phagocytosis-promoting activity for human polymorphonuclear leukocytes and augmented the production of superoxide anion by human peripheral leukocytes.