L-phosphinothricin (L-PPT) is an efficient broad-spectrum herbicide. To realize the multi-enzyme catalytic preparation of L-PPT, we constructed an engineered strain Escherichia coli YM-1 for efficient expression of D-amino acid transaminase, which could catalyze the generation of the intermediate 2-oxo-4-[(hydroxymethylphosphonyl)] butyric acid (PPO) from D-phosphinothricin (D-PPT). In addition, E. coli pLS was constructed to co-express glutamate dehydrogenase and glucose dehydrogenase, which not only catalyzed the generation of L-PPT from PPO but also regenerated the coenzyme nicotinamide adenine dinucleotide phosphate (NADPH). A fed-batch fermentation process was then established for E. coli YM-1 and pLS, and the apparent activities of D-amino acid transaminase and glutamate dehydrogenase were increased by 22.68% and 100.82%, respectively, compared with those in shake flasks. The process parameters were optimized for the catalytic preparation of L-PPT by whole-cell cascade of E. coli YM-1 and pLS with D, L-PPT as the substrate. After reaction for 8 h, 91.36% conversion of D-PPT was achieved, and the enantiomeric excess of L-PPT reached 90.22%. The findings underpin the industrial production of L-PPT.
Escherichia coli/enzymology* ; Aminobutyrates/metabolism* ; Glutamate Dehydrogenase/biosynthesis* ; Glucose 1-Dehydrogenase/biosynthesis* ; Herbicides/metabolism* ; Multienzyme Complexes/metabolism* ; Transaminases/metabolism* ; Phosphinic Acids/metabolism*

Objective To make a preliminary evaluation of the degradation of AZ31 bioabsorbable magnesium alloy stent implanted in the abdominal aorta of experimental rabbits.Methods Twelve AZ31 biodegradable magnesium alloy stents were separately deployed in the infrarenal abdominal aortas of twelve New Zealand white rabbits.Every three experimental rabbits were sacrificed each time at one,two,three and four months after the procedure of stenting.The stenting segment of the aortas were harvested,radiographod and sent for pathologic examination to observe the degradable performance of the stent.Results All animals survived form the operation in the scheduled follow-up period.Radiographically and pathologically,the stents were fully expanded with perfect shape one month after the procedure,and part of the stent struts began to be degraded and fractured in two months,resulting in the loss of its supporting function.Three months after the implantation most stents were corroded.and in four months all the stents become completely destroyed.The estimating time for producing complete degradation of AZ31 magnesium alloy stents in rabbit's aorta was 104.5 days.Conclusion AZ31 bioabsorbable magnesium alloy stents implanted in rabbit abdominal aorta will lose their radial force in two months.How to prolong the functioning time of the implanted stents is the next research target.