Theanine synthesized by immobilizing Pseudomonas nitroreducens LY in nanofibrous membranes

L-theanine synthesis using γ-glutamyl transpeptidase from Bacillus licheniformis ER-15

Recombinant γ-glutamyl transpeptidase (rBLGGT) from Bacillus licheniformis ER-15 was purified to homogeneity by ion-exchange chromatography. Molecular masses of large and small subunits were 42 and 22 kDa, respectively. The enzyme was optimally active at pH 9.0 and 60 °C and was alkali stable. K(m) and V(max) for γ-glutamyl-p-nitroanilide hydrochloride were 45 μM and 0.34 mM/min, respectively. L-Theanine synthesis was standardized using a one variable at a time approach followed by response surface methodology, which resulted in approximately 85-87% conversion of L-glutamine to L-theanine within 4 h. The standardized reaction contained 80 mM L-glutamine, 600 mM ethylamine, and 1.0 U/mL rBLGGTin 50 mM Tris-Cl (pH 9.0) at 37 °C. Similar conversions were also obtained with the enzyme immobilized in calcium alginate. Using immobilized enzyme, 35.2 g of L-theanine was obtained in three cycles of 1 L each. The product was purified by Dowex 50W X 8 hydrogen form resin and was confirmed by HPLC and proton NMR spectroscopy.

Pyrimidine nucleotide synthesis in Pseudomonas nitroreducens and the regulatory role of pyrimidines

Control of pyrimidine biosynthesis in the commercially important, hydrocarbon-utilizing bacterium Pseudomonas nitroreducens ATCC 33634 was investigated. When glucose-grown wild-type cells were supplemented with uracil or orotic acid, the pyrimidine biosynthetic activities were depressed. Pyrimidine limitation of glucose-grown cells of an orotate phosphoribosyltransferase mutant caused aspartate transcarbamoylase and dihydroorotase activities to increase by about 4-fold while the other enzyme activities about doubled. In succinate-grown phosphoribosyltransferase mutant cells subjected to pyrimidine limitation, transcarbamoylase and dehydrogenase activities rose by about 5-fold while dihydroorotase activity more than tripled. In an OMP decarboxylase mutant, pyrimidine limitation of glucose-grown cells increased transcarbamoylase, dihydroorotase, dehydrogenase and phosphoribosyltransferase activities by 4-, 10-, 6- and 3.8-fold, respectively. Pyrimidine limitation of the succinate-grown decarboxylase mutant cells increased aspartate transcarbamoylase or dihydroorotase by more than 4-fold and the other activities by about 2-fold. Pyrimidine biosynthetic enzyme synthesis appeared to be regulated by pyrimidines with the regulation being influenced by the carbon source present. Aspartate transcarbamoylase activity in Ps. nitroreducens was regulated at the level of enzyme activity since the enzyme was strongly inhibited by UDP, pyrophosphate, ATP and ADP. Overall, the regulation of pyrimidine biosynthesis in Ps. nitroreducens can be used to differentiate it from other taxonomically related species of Pseudomonas.

Application of novel electrospun nanofibrous membranes with different modifications for immobilising glutamine synthetase

BACKGROUND

Theanine synthesis is of interest because of the physiological and pharmacological benefits of theanine. Glutamine synthetase (GS, EC 6.3.1.2) from Pseudomonas taetrolens can be used for theanine biosynthesis. In this study, GS was immobilised in polyvinyl alcohol electrospun nanofibres, and the properties of immobilised GS with different solidifying modifications were studied.

RESULTS

Electrospinning is a good method for enzyme immobilisation. When carbon nanotubes were used as an adsorbent, the activity retention of immobilised GS was 92.3%. With glutaraldehyde as a crosslinker, the enzyme activity retention was only 50.7%; however, by adding collagen or peptide to the electrospinning solution with glutaraldehyde, the activity retention could be improved to 85.9 or 59.6% respectively. Scanning electron micrographs showed that the modifiers induced morphological changes in the nanofibres. The optimum pH and temperature of immobilised GS also changed. In addition, the reusability and storage stability of immobilised GS with glutaraldehyde were much better than those of immobilised GS with carbon nanotubes.

CONCLUSION

A novel method has been established in this study for the immobilisation of GS in electrospun nanofibrous membranes. Carbon nanotubes and glutaraldehyde enhanced the immobilisation, while collagen or peptide inclusion could recover the activity loss caused by glutaraldehyde. The obtained immobilised enzyme achieved high reusability and storage stability.