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

aswell as impede large scale processing. To increase membrane permeability and cellbound glutamate decarboxylase (GAD) activity of recombinant

Escherichia coli

(BL21(DE3)-pET28a-

gadB

) 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)-pET28a-

gadB

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)-pET28a-

gadB

and total cell-bound GAD activity per m

illiliter of culture was enhanced by 6.24- and 3.64-fold

respectively. Treatment of BL21 (DE3)-pET28a-

gadB

cells with 5 μg·ml

-1

ampicillin 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 10th cycle produced by immobilized and permeabilized cells remained 46% of the first cycle. GAD activity of the immobilized

permeabilized cells remained over 90% after 30 days of storage at 4℃.