Z-L-valyl-L-glycine

Mutant derivatives of Escherichia coli K-12 deficient in several peptidases have been obtained. Mutants lacking a naphthylamidase, peptidase N, were isolated by screening for colonies unable to hydrolyze L-alanine beta-naphthylamide. Other mutants were isolated using positive selections for resistance to valine peptides. Mutants lacking peptidase A, a broad-specificity aminopeptidase, were obtained by selection for resistance to L-valyl-L-leucine amide. Mutants lacking a dipeptidase, peptidase D, were isolated from a pepN pepA strain by selection for resistance to L-valyl-glycine. Starting with a pepN pepA pepD strain, selection for resistance to L-valyl-glycyl-glycine or several other valine peptides produced mutants deficient in another aminopeptidase, peptidase B. Mutants resistant to L-valyl-L-proline lack peptidase Q, an activity capable of rapid hydrolysis of X-proline dipeptides. Using these selection procedures, a strain (CM89) lacking five different peptidases has been isolated. Although still sensitive to valine, this strain is resistant to a variety of valine di- and tripeptides. The ability of this strain to use peptides as sources of amino acids is much more restricted than that of wild-type E. coli strains. Strains containing only one of the five peptidases missing in CM89 have been constructed by transduction. The peptide utilization profiles of these strains show that each of the five peptidases can function during growth in the catabolism of peptides.

Recently, it has been demonstrated that kokumi substances such as glutathione are perceived through the calcium-sensing receptor (CaSR), and screening by CaSR assay and sensory evaluation has shown that γ-glutamyl-valyl-glycine (γ-Glu-Val-Gly) is a potent kokumi peptide. In this study, γ-Glu-Val-Gly contents in various brewed alcoholic beverages were investigated. Contents of γ-Glu-Val-Gly in four brands of wine, four brands of rice wine (sake) and eight brands of beer were analyzed by high performance liquid chromatography-tandem mass spectrometry followed by derivatization with 6-aminoquinoyl-N-hydroxysuccinimidyl-carbamate. The analyses indicated that γ-Glu-Val-Gly was present in all of eight beer samples at concentrations in the range of 0.08-0.18 mg/L, although the peptide was not detected in any wine or rice wine samples. These results suggest that amongst the brewed beverages tested, beer contains γ-Glu-Val-Gly, and that γ-Glu-Val-Gly is widely distributed in beer.