The application of L‐glutaminase for the synthesis of the immunomodulatory γ‐D‐glutamyl‐L‐tryptophan and the kokumi‐imparting γ‐D‐glutamyl peptides

Glutaminase of Bacillus amyloliquefaciens has been used to synthesize the immunomodulatory γ‐D‐glutamyl‐L‐tryptophan (γ‐D‐Glu‐L‐Trp) and the kokumi‐active γ‐D‐glutamyl peptides. The optimum yield of γ‐D‐Glu‐L‐Trp was 55.76 mM in corresponding to a minimum yield of by‐product (γ‐D‐Glu‐γ‐D‐Glu‐L‐Trp) in the presence of 75 mM D‐Gln and 100 mM L‐Trp. The glutaminase has a low K(m) values for the donors (D‐Gln and L‐Gln:5.53 and 0.98 mM), but high ones for the acceptors (L‐Trp, L‐Phe, L‐Met, L‐Val and γ‐[D‐Glu](() (n) (=1,2,3))‐L‐Val/L‐Phe/L‐Met, ranging from 32.51 to 193.05 mM). The highest K(m) value appearing when n = 2 (γ‐[D‐Glu](() (n) (=0,1,2))‐L‐Val/L‐Phe/L‐Met) suggested the rising difficulty for synthesis when the number of donor increases in the reaction mixtures. The γ‐[D‐Glu](() (n) (=1,2,3))‐L‐Val/L‐Phe/L‐Met at 5 mM can impart the blank chicken broth an enhancing monthfulness, thickness, and umaminess taste.