Biosci. Biotechnol. Biochem., 71 (10), 2618–2621, 2007 Communication Soymorphins, Novel Opioid Peptides Derived from Soy -Conglycinin -Subunit, Have Anxiolytic Activities
y Kousaku OHINATA, Shun AGUI, and Masaaki YOSHIKAWA
Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Gokasho Uji, Kyoto 611-0011, Japan
Received August 13, 2007; Accepted September 13, 2007; Online Publication, October 7, 2007 [doi:10.1271/bbb.70516]
Based on the amino acid sequence YPFV found in the 1 µM soy -conglycinin -subunit, which is common to an 3 µM opioid peptide human -casomorphin-4, peptides YPF- 10 µM VV, YPFVVN, and YPFVVNA were synthesized ac- cording to their primary structure. On guinea pig ileum (GPI) assay, they showed opioid activity (IC50 = 6.0, 9.2 and 13 M respectively) more potent than human - casomorphins, and were named soymorphins-5, -6, and -7, respectively. Their opioid activities on mouse vas deferens (MVD) assay were less potent than on GPI assay, suggesting that they are selective for the opioid receptor. Human -casomorphin-4 and soymorphin-5 1 min were released from the soy 7S fraction ( -conglycinin) by the action of gastrointestinal proteases. Soymor- Fig. 1. Typical Opioid Activity of Soymorphin-5 (YPFVV) on phins-5, -6, and -7 had anxiolytic activities after oral Guinea Pig Ileum (GPI) Assay. administration at doses of 10–30 mg/kg in the elevated Ileum-contracting activity by electrical stimulation was dose- dependently inhibited by soymorphin-5 at doses of 1–10 mM. plus-maze test in mice.
Key words: opioid peptide; opioid receptor; anxiolytic effect; soy protein; -conglycinin -subunit GPI assay. Figure 1 indicates the typical suppressive effect of YPFVV on electrically stimulated contractions Opioid is a chemical substance that has morphine-like on GPI assay. YPFVVN and YPFVVNA also dose- action. An opioid peptide, bovine -casomorphin-7 dependently inhibited ileum contractions (data not (YPFPGPI), isolated from casein peptone, was the first shown). These results suggest that YPFVV, YPFVVN, example of bioactive peptides released from food and YPFVVNA have opioid activities; they were named proteins.1) We have reported that human -casomor- soymorphins-5, -6, and -7 respectively. The opioid phin-4 (YPFV) and related peptides derived from human activities of synthetic peptides derived from the soy - -casein also have opioid activities, though they are less conglycinin -subunit are summarized in Table 1. The 2) potent than their bovine counterparts. Of three soy - IC50 values of soymorphins-5, -6, and -7 on GPI assay 0 conglycinin subunits ( , , and ),3) the -subunit has were 6.0, 9.2, and 13 mM respectively, and their opioid the human -casomorphin-4 sequence (YPFV). Longer activities were more potent than those of human - peptides, YPFVV, YPFVVN, and YPFVVNA, were casomorphin-4, -5, and -6 (IC50 = 20, 14, and 25 mM, synthesized according to the primary structure of the - respectively). There are three types of opioid receptors: conglycinin -subunit by the Fmoc strategy, and their , , and .5,6) The opioid activities of soymorphins were opioid activities were tested by guinea pig ileum (GPI) larger on GPI assay than those on MVD assay, and mouse vas deferens (MVD) assay, as previously suggesting that these peptides are selective for the - described.4) All experiments were approved by the opioid receptor. The affinities for the -opioid receptor Kyoto University Ethics Committee for Animal Re- were 17, 39, and 47 mM respectively, and the rank order search Use. of their affinities for the receptor was consistent with The peptides were found to have opioid activities on that of the opioid activities on GPI assay. Taking all this
y To whom correspondence should be addressed. Tel: +81-774-38-3725; Fax: +81-774-38-3774; E-mail: [email protected] Abbreviations: i.p., intraperitoneal; p.o., per os; GPI, guinea pig ileum; MVD, mouse vas deferens; LAP, leucine aminopeptidase Soymorphins Have Anxiolytic Activity 2619 Table 1. Opioid Activities of Soymorphin-5, -6, and -7 Derived from the Soy -Conglycinin -Subunit by Guinea Pig Ileum (GPI) and Mouse Vas Deferens (MVD) Assays, and Their Affinities for the -Opioid Receptor
Opioid activity (IC50, mM) Affinity (IC50, mM) Peptide Sequence GPI ( ) MVD ( ) receptor Soymorphin-5 YPFVV 6.0 50 17 Soymorphin-6 YPFVVN 9.2 32 39 Soymorphin-7 YPFVVNA 13 50 47