EFFICIENT RELEASE OF THERMOSTABLE BETA-GALACTOSIDASE BY GLYCINE ADDITION AND THERMAL-TREATMENT OF ESCHERICHIA-COLI-CELLS

Efficient release of thermostable beta-galactosidase from a recombinant Escherichia coli by the addition of glycine to the culture broth and subsequent thermal treatment was investigated. The enzyme release rate was strongly dependent on glycine concentration. The enzyme release rate was almost proportional to glycine concentrations up to 2% in phosphate buffer; however, inactivation of the enzyme was not observed following incubation for up to 3 h at 70 degrees C even in the presence of 10% glycine. In a preliminary experiment, severe thermal inactivation was observed in the presence of polyethylene glycol (PEG), but glycine was able to suppress the inactivation. Thermal treatment of the cell suspension was effective for the improvement of the enzyme release rate. In the absence of glycine, the enzyme release rate was low at 37 and 45 degrees C, even though the initial release rate was high at 0.5 h and 60 degrees C. The combination of thermal treatment and addition of glycine to the cell suspension significantly improved the initial enzyme release rate and the amount of enzyme released to the extracellular fraction at 37 and 45 degrees C was as high as that at 60 degrees C during a 2-h incubation.