Abstract
An E. coli strain, SH209, harboring pLC9-12 exhibited 5- to 6-fold higher γ-glutamyltranspeptidase activity than the wild-type strain, at each growth temperature tested. Maximum activity was observed at 20-25°C, as was observed with the wild type. A homogeneous enzyme preparation was obtained from the periplasmic fraction of the strain by a simple three-step method. The conditions for γ-glutamyl-DOPA synthesis from L-glutamine and L-DOPA were investigated using the enzyme preparation. Under the best conditions, the maximal yield of 79%, equivalent to 158 mM (51.5 g/1) of γ-glutamyl-DOPA as to both substrates, was obtained. γ-Glutamyl-DOPA was isolated from the reaction mixture and identified using an amino acid analyzer after hydrolysis with HC1 or γ-glutamyltranspeptidase.
