In order to facilitate the preparation of paeoniflorin(PF)and albiflorin(AF),two chief bioactive constituents in Paeonia lactiflora Pall(PL),induction and culture of callus from PL were studied.With a modified woody plant medium supplemented with 0.5 mg·L-16-benzylaminopurine,1.0 mg·L-1naphthylacetic acid,0.1 mg·L-1thidiazuron and 30 g·L-1sucrose,callus was induced from four kinds of explants:leaf,stems,petiole,and root.The potency to form callus varies between different explants and leaf explants exhibits the highest capacity(100%).On the other hand,root-derived callus(R-callus)produces the highest level of total amount of PF and AF,31.8 mg·g-1dry mass,which is higher than the corresponding level in the root of field cultivated PL.Furthermore,the time needed is only 40 days,remarkably shorter than the cultivation time of PL,about 4–5 years.Higher accumulation levels of PF and AF with shorter production time indicate that callus culture of PL is a promising powerful tool for production of PF and AF in the future.
Glutamate decarboxylase(GAD, EC4.1.1.15) can catalyze the decarboxylation of L-glutamate to form γ-aminobutyrate(GABA), which is in great demand in some foods and pharmaceuticals. In our previous study,gad, the gene coding glutamate decarboxylase from Lactobacillus brevis CGMCC 1306, was cloned and its soluble expression was realized. In this study, error-prone PCR was conducted to improve its activity, followed by a screening. Mutant Q51 H with high activity [55.4 mmol·L-1·min-1·(mg protein)-1, 120% higher than that of the wild type at p H 4.8] was screened out from the mutant library. In order to investigate the potential role of this site in the regulation of enzymatic activity, site-directed saturation mutagenesis at site 51 was carried out,and three specific mutants, N-terminal truncated GAD, Q51 P, and Q51 L, were identified. The kinetic parameters of the three mutants and Q51 H were characterized. The results reveal that aspartic acid at site 88 and N-terminal domain are essential to the activity as well as correct folding of GAD. This study not only improves the activity of GAD, but also sheds new light on the structure–function relationship of GAD.
The activity of whole-cell biocatalysts is strongly compromised by the cell envelope, which is a permeability barrier against the diffusion of substrates and products. Although common chemical or physical permeabilization methods used in cultured cells enhance cell permeability, these methods inevitably add several extra processing steps after cell cultivation, as well as impede large scale processing. To increase membrane permeability and cellbound glutamate decarboxylase(GAD) activity of recombinant Escherichia coli(BL21(DE3)-p ET28a-gad B) cells without the need for an additional permeabilization step, we investigated the permeabilizing effects of adding cell wall synthesis inhibitors or surfactants to the culture media. Ampicillin was the most effective at improving cell-bound GAD activity of the BL21(DE3)-p ET28a-gad B, although it decreased the cell biomass yield. The best permeabilization effect was observed using an ampicillin concentration of 5 μg·ml-1. Using this concentration,the cell biomass did decrease by 40.58%, but the cell-bound GAD activity of BL21(DE3)-p ET28a-gad B and total cell-bound GAD activity per milliliter of culture was enhanced by 6.24- and 3.64-fold, respectively. Treatment of BL21(DE3)-p ET28a-gad B cells with 5 μg·ml-1ampicillin resulted in structural changes to the cell envelope,but did not substantially affect GAD expression. By entrapping the ampicillin-treated cells in an open pore gelation matrix, which is a polymer derived from polyvinyl alcohol(PVA), alginate, and boric acid, the transformation rate of γ-aminobutyric acid(GABA) at the 10 th cycle produced by immobilized and permeabilized cells remained 46% of the first cycle. GAD activity of the immobilized, permeabilized cells remained over 90% after30 days of storage at 4 °C.
Weirui ZhaoSheng HuJun HuangPiyu KeShanjing YaoYinlin LeiLehe MeiJinbo Wang
