Cascade Synthesis of L‑Homoserine Catalyzed by Lyophilized Whole Cells Containing Transaminase and Aldolase Activities: The Mathematical Modeling Approach

Aldolase and transaminase coexpressed inEscherichia colicells and lyophilized (i.e., lyophilized whole-cell biocatalyst (LWCB)) were used as biocatalysts for the one-pot cascade synthesis of l-homoserine with substrate cycling. The kinetic analysis of enzymes within lyophilized cells was performed to evaluate the behavior of the system. The best result among the performed fed-batch reactor experiments achieved was 640.8 mM (76.3 g L^-1) of lhomoserine with a volume productivity of 2.6 g L^-1h^-1. This is comparable with the results of the same cascade synthesis using cell-free extracts (CFEs) and significantly better than the reports in the literature applying fermentation technology. The approach applied here can serve as guidance for the design of microbial cells with an optimal ratio of expressed enzymes that act as biocatalysts in the cascade, resulting in lower biocatalyst cost, no need for the addition of expensive coenzymes, and enhanced enzyme stability as compared with cell-free extracts.