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*

In the present study, the correlated activities of adjacent ganglion cells of transient subtype in response to full-field white light stimulation were investigated in the chicken retina. Pharmacological studies and cross-correlation analysis demonstrated that application of the GABA(A) receptor antagonist bicuculline (BIC) significantly down-regulated the correlation strength while increasing the firing activities. Meanwhile, application of the GABA(A) receptor agonist muscimol (MUS) potentiated the correlated activities while decreasing the firing rates. However, application of the GABA(C) receptor antagonist (1,2,5,6-Tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA) did not have a consistent influence on either the firing rates or the correlation strength. These results suggest that in the chicken retina, correlated activities among neighborhood transient ganglion cells can be increased while firing activities are reduced with the activation of GABA(A) receptors. The GABA(A)-receptor-mediated inhibitory pathway may be critical for improving the efficiency of visual information transmission.
Action Potentials ; Animals ; Bicuculline ; pharmacology ; GABA-A Receptor Antagonists ; pharmacology ; Mice ; Muscimol ; pharmacology ; Phosphinic Acids ; pharmacology ; Pyridines ; pharmacology ; Receptors, GABA-A ; metabolism ; Retina ; physiology ; Retinal Ganglion Cells ; physiology ; gamma-Aminobutyric Acid