FIG. 3.

d-Phe-Pro-DKP formation in the heterologous host E. coli. Samples taken at certain time points (1 to 8 h after induction) and derived from cultures grown in LB rich medium (A) and M9 minimal medium (B) were analyzed by HPLC. Compound B coeluted with the chemical standard and corresponds to the expected d-Phe-Pro-DKP as verified by HPLC-MS (data not shown). The time-dependent production of d-Phe-Pro-DKP in LB (dots and solid line) and M9 (open circles and dashed line) media was normalized to OD₆₀₀ (C). Defined quantities of d-Phe-Pro-DKP (chemical standard) were analyzed by HPLC in order to establish a calibration curve (D). All samples were taken and analyzed in triplicate.