Development of immobilization and drying methods of enzymes on support particles for enzymatic gas-phase reactions

摘要

In this research work, two mesophilic alcohol dehydrogenases namely baker’s yeast alcohol dehydrogenase (YADH) and Lactobacillus brevis alcohol dehydrogenase (LBADH) and one thermophilic alcohol dehydrogenase namely Thermoanaerobacter species alcohol dehydrogenase (ADH T) were immobilized by physical adsorption method. The effects of various immobilization and drying process parameters on the residual activity and the protein loading of the immobilized enzyme preparation were studied and thereby different optimum preparations were observed for different enzymes. Under the optimum immobilization conditions the residual activity achieved with YADH, LBADH, and ADH T was about 80%, 316%, and 325%, respectively. The hypothesis of bubble nucleation as a cause for loss of enzyme activity during the low pressure drying process was verified. The effects of various gas-phase reaction conditions on the initial reaction rate and the half-life of the optimized preparations were also studied. It was observed that addition of a suitable buffer (50 mM phosphate buffer, pH 7) or an optimum amount of sucrose (5 times greater than the amount of protein on weight basis) during the enzyme immobilization enhanced the half-life of the immobilized enzymes in the gas-phase reaction. Water activity significantly influenced the initial reaction rate and the half-life of the immobilized enzyme preparations in the gas-phase reaction. The optimum water activity found for LBADH and ADH T was the same (0.55). Under the optimized immobilization and gas-phase reaction conditions the thermo-stability of the ADH enzymes was enhanced tremendously. The space-time yield of (R)-phenylethanol was about 1000 g l-1 d-1 with LBADH and the space-time yield of (S)-phenylethanol was about 600 g l-1 d-1 with ADH T. The total turn over number of LBADH was about and the same of ADH T was about.