Presence of aspartic dipeptides with β peptide bond and/or D-aspartyl residue in rat blood after ingestion of porcine liver protein hydrolysate

Background: Animal experiments have demonstrated that oral administration of a porcine liver protein hydrolysate (LPH) ameliorates alcohol-induced liver toxicity, as well as exercise- and concanavalin A-induced low locomotor activity in mice. The peptides responsible for the beneficial effect have not yet been identified. Recently, presence of food-derived peptides in human blood has been detected post ingestion of other food protein hydrolysates. These peptides are prolyl, hydroxyprolyl, or pyroglutamyl di- and tri-peptides, and resist exopeptidase digestion. Some of these peptides exert significant biological roles in vitro and in vivo, which have been associated with the biological response post ingestion. The objective of the present study was to identify the food-derived peptides in rat blood after ingestion of LPH.Results: In the in vitro exopeptidase digest of LPH, pyroglutamyl, prolyl, hydroxyprolyl, and aspartic dipeptides were identified. The aspartic peptides (Asp-Val, Asp-Ile, Asp-Leu, and Asp-Phe) showed multiple peaks by LC-MS/MS, indicating the presence of isomers. Four isomers with L- and D-aspartyl residues, and α and β peptide bonds were present in each sequence. After administration of LPH, the amounts of unusual aspartic dipeptides with β peptide bond and/or D-aspartyl residue significantly increased in rat plasma, while those of the other usual aspartic peptides did not.Conclusions: Racemization and isomerization of aspartyl residues in peptides occur during the preparation of LPH or following its digestion. The unusual aspartic peptides have a potential for carrying out diverse biological activities.Key words: Peptide, food protein hydrolysate, aspartic, isopeptide, bioavailability, D-amino acid

Thermal Synthesis of Polypeptides from N-Butyloxycarbonyl Oligopeptides Containing Aspartyl Residue at C-Terminus

The thermal reactions of amino acids have been investigated for pure organic synthesis, materials preparation in industry, and prebiotic chemistry. N-t-Butyloxycarbonyl aspartic acid (Boc-Asp) releases 2-butene and carbon dioxide upon heating without solvents. The resulting mixture of the free molten aspartic acid was dehydrated to give peptide bonds. This study describes the thermal reactions of N-t-butyloxycarbonyl peptides (Boc-Gly-L-Asp, Boc-L-Ala-L-Asp, Boc-L-Val-L-Asp, and Boc-Gly-Gly-L-Asp) having an aspartic residue at the carboxyl terminus. The peptides were deprotected upon heating at a constant temperature between 110 and 170°C for 1 to 24 h to afford polypeptides in which the average molecular weight reached 7800.

Modification of the volatile compound profile of cheese, by aLactococcus lactisstrain expressing a mutant oligopeptide binding protein

Lactococcus lactisstrain AMP2I expresses OppA(D471R), a mutant oligopeptide binding OppA protein in which the aspartyl residue at position 471 was replaced by arginine. As a consequence of a different peptide transport in this strain, experimental Hispánico cheese made withLc. lactisAMP2I had a higher content of total free amino acids than control cheese made withLc. lactisAMP1I, an isogenic strain expressing wild-type OppA (Picon et al. 2005, 2007). In this work higher levels of diketones, hydroxy-ketones and, to a lesser extent, branched chain aldehydes were recorded for experimental cheese compared with control cheese. These differences levelled off as ripening proceeded. Strong correlations support the hypothesis that the increased levels of these volatile compounds in cheese made withLc. lactisAMP2I are linked to higher concentrations of free amino acids threonine, valine and leucine.