2.1 Chemicals, plasmids, and culture media
Lactose, galactitol, NADH, NADPH, NAD+, and NADP+ were purchased from Coolaber Co. Ltd. (Beijing, China). The five types of WP were obtained from Qianwei Biotech (Shanghai, China), Miaolingziwei Biotech (Henan, China), Wanbang Biotech (Henan, China), Gushuo Biotech (Henan, China), and Fengtai Biotech (Shandong, China). The β -galactosidase with ~1.2 × 105 U was purchased from Weilan Biotech (Shandong, China). The KOD-Plus-Mutagenesis Kit was purchased from Toyobo Co., Ltd. (Osaka, Japan). ABclonal MultiF Seamless Assembly was purchased from ABclonal Technology Co., Ltd. (Wuhan, China). pET-32a was purchased from Invitrogen (Carlsbad, CA, USA). Ampicillin and isopropyl-beta-D-thiogalactopyranoside (IPTG) were purchased from Gen-View Scientific Inc. (El Monte, CA, USA).Escherichia coli DH5α and E. coli BL21 (DE3) were purchased from Tsingke Biotechnology Co., Ltd. and TransGen Biotech (Beijing, China), respectively. Primers were synthesized by Ruibiotech Co., Ltd. (Beijing, China). Phanta®Max Super-Fidelity DNA Polymerase was purchased from Vazyme Biotech Co., Ltd. (Nanjing, China). Any other chemicals used in this study were analytical grade and obtained commercially unless otherwise noted.