Soushi Sonoda

Rubiscolin, a δ selective opioid peptide derived from plant Rubisco

We found that the sequences YPLDL and YPLDLF in the large subunit of spinach D‐ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) met the structure YP‐aliphatic amino acid which might have opioid activity. We then synthesized these peptides to test their opioid activity. The IC50 of these peptides in mouse vas deferens assay were 51.0 μM and 24.4 μM, respectively, and those in δ receptor binding assay using [3H]deltorphin II as radioligand were 2.09 μM and 0.93 μM, respectively. Both peptides were selective for δ receptor. We named them rubiscolin‐5 and ‐6, respectively. Rubiscolin‐5 and ‐6 have antinociceptive activity in mice after i.c.v. or oral administration. The enzymatic conditions to release rubiscolin were investigated using both spinach Rubisco and synthetic fragment peptides. This is the first example of bioactive peptides derived from plant Rubisco.

Antinociception induced by β-lactotensin, a neurotensin agonist peptide derived from β-lactoglobulin, is mediated by NT2 and D1 receptors

Abstract In this study, we examined the antinociceptive effect of β-lactotensin, a neurotensin agonist that has been isolated from the chymotrypsin digest of β-lactoglobulin as an ileum-contracting peptide. β-Lactotensin showed naloxone-insensitive antinociceptive activity by the tail-pinch test after i.c.v. (200 nmol/mouse) or s.c. (300 mg/kg) administration in ddY mice. Tolerance was not developed to antinociception induced by β-lactotensin after repeated s.c. administration for 5 days. The antinociceptive activity of β-lactotensin was blocked by treatment with the neurotensin NT2 receptor antisense ODN, while treatment with the NT1 receptor antisense ODN had no effect. The antinociceptive activity was also blocked by a dopamine D1 receptor antagonist, SCH23390 (1 μg/mouse, i.c.v.), while a D2 receptor antagonist, raclopride (0.5 μg/mouse, i.c.v.), did not block the activity. These results indicate that the antinociceptive activity of β-lactotensin is mediated by NT2 and D1 receptors.

Structure-activity relationship of rubiscolins as δ opioid peptides

Abstract To study the structure–activity relationship of rubiscolins (YPLDLF and YPLDL), δ opioid peptides derived from the spinach Rubisco, we substituted the amino acid residues and evaluated their activities by mouse vas deferens (MVD) and guinea pig ileum (GPI) assays as well as receptor affinity. Replacement of Leu 3 with Ile and Met in rubiscolin-6 potentiated the δ opioid activity by about four times in MVD assay. Asp 4 cannot be replaced by Ala, Glu or His. The original Leu 5 was optimal, while substitution of Phe 6 with Val potentiated its δ opioid activity by more than 10 times. The most potent derivative we obtained was YPMDLV, which was nearly 20 times more potent than rubiscolin-6 in MVD assay. The derivatives thus obtained showed higher δ receptor affinity and more potent antinociceptive activity than rubiscolins.

Enterostatin (APGPR) enhances memory consolidation in mice.

Enterostatin (APGPR) is a pentapeptide released from its precursor protein, procolipase. We found for the first time that enterostatin has memory-enhancing activity. Enterostatin enhanced memory consolidation after central or oral administration at a dose of 10 nmol/mouse or 300 mg/kg, respectively, in a step-through type passive avoidance test in mice. The memory-enhancing activity of enterostatin was inhibited by pretreatment with lorglumide, an antagonist for cholecystokinin 1 (CCK1) receptor. However, enterostatin had no affinity for CCK receptors. These results suggest that enterostatin improves memory retention through CCK release.