Acorbine, a Corbicula japonica-derived tripeptide containing non-proteinogenic amino acids, suppresses ethanol-induced liver injury.

Since ancient times, Corbicula extract has been believed in Japan to have hepatoprotective effects, but it remains unclear whether these claims are true, and if so, which component is responsible for hepatoprotection. In this study, we showed that Corbicula extract exerted a protective effect against liver damage. Recent work identified acorbine (ß-alanyl-ornithyl-ornithine), a novel tripeptide containing non-proteinogenic amino acids, in the extract of Corbicula japonica. Synthesized acorbine cured alcohol-induced liver damage in mice. In addition, acorbine purified from Corbicula extract exerted a protective effect against alcohol-induced hepatotoxicity in a culture liver model derived from mouse ES/iPS cells. Thus, acorbine is one of the components of Corbicula extract that protects hepatocytes against ethanol-induced death.

A novel ornithine-containing tripeptide isolated from the extract of the brackish-water bivalve Corbicula japonica.

Previous studies have demonstrated that frozen preparations of the brackish-water bivalve Corbicula japonica significantly increase the content of free ornithine found in its extracts. Here we report a novel ornithine-containing tripeptide commonly found in C. japonica, which is believed to be the source of increased free ornithine. The new peptide, named acorbine, was isolated from extracts of this bivalve obtained using ultra-filtration and gel permeation chromatography. Acorbine is comprised of N(2)-[N(2)-(beta-alanyl)-L-ornithyl]-L-ornithine as determined by amino acid composition analysis, N- and C-terminal amino acid analyses, proton nuclear magnetic resonance spectrometry, and chirality analysis of the ornithine residue. The total amount of beta-alanine and ornithine in the extract remained constant regardless of the temperature at which the bivalve was processed. The amount of free beta-alanine and ornithine increased significantly when the bivalve was frozen, with a corresponding decrease in peptidic beta-alanine and ornithine. The results suggest that changing the growth conditions triggers tripeptide proteolysis within the bivalve, which ultimately manifests in increased free beta-alanine and ornithine.

Influence of low-temperature processing of the brackish-water bivalve, Corbicula japonica, on the ornithine content of its extract.

The ornithine content of an extract of the brackish-water bivalve, Corbicula japonica, increased when the bivalve was frozen. It was not influenced by the period of freezing. This phenomenon was not apparent in the scallop, little-neck clam, or hard clam. We applied various low-temperature conditions for processing the bivalve from 4 degrees C to -10 degrees C and measured the ornithine content of each extract. The ornithine content was maximized by processing at - 4 degrees C. The increase in this ornithine content was reduced when the bivalve was stored at 5 degrees C or 15 degrees C after processing at - 4 degrees C, this decrease being reversed when the bivalve was again processed at - 4 degrees C after warming. Low-temperature processing of the brackish-water bivalve therefore increased the ornithine content of the extract.

Purification, characterization and molecular cloning of tyrosinase from the cephalopod mollusk, Illex argentinus.

Tyrosinase (monophenol, L-DOPA:oxygen oxidoreductase) was isolated from the ink of the squid, Illex argentinus. Squid tyrosinase, termed ST94, was found to occur as a covalently linked homodimeric protein with a molecular mass of 140.2 kDa containing two copper atoms per a subunit. The tyrosinase activity of ST94 was enhanced by proteolysis with trypsin to form a protein, termed ST94t, with a molecular mass of 127.6 kDa. The amino acid sequence of the subunit was deduced from N-terminal amino acid sequencing and cDNA cloning, indicating that the subunit of ST94 is synthesized as a premature protein with 625 amino acid residues and an 18-residue signal sequence region is eliminated to form the mature subunit comprised of 607 amino acid residues with a deduced molecular mass of 68,993 Da. ST94 was revealed to contain two putative copper-binding sites per a subunit, that showed sequence similarities with those of hemocyanins from mollusks, tyrosinases from microorganisms and vertebrates and the hypothetical tyrosinase-related protein of Caenorhabditis elegans. The squid tyrosinase was shown to catalyze the oxidation of monophenols as well as o-diphenols and to exhibit temperature-dependency of o-diphenolase activity like a psychrophilic enzyme.