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β-Galactosidase from the fungus Talaromyces thermophilus CBS 236.58 was immobilized by covalent attachment onto the insoluble carrier Eupergit C with a high binding efficiency of
95%. Immobilization increased both activity and stability at higher pH values and temperature when compared with the free
enzyme. Especially the effect of immobilization on thermostability is notable. This is expressed by the half-lifetime of the
activity at 50°C, which was determined to be 8 and 27 h for the free and immobilized enzymes, respectively. Although immobilization
did not significantly change kinetic parameters for the substrate lactose, a considerable decrease in the maximum reaction
velocity V
max was observed for the artificial substrate o-nitrophenyl-β-d-galactopyranoside (oNPG). The hydrolysis of both oNPG and lactose is competitively inhibited by the end products glucose
and galactose. However, this inhibition is only very moderate as judged from kinetic analysis with glucose exerting a more
pronounced inhibitory effect. It was evident from bioconversion experiments with 20% lactose as substrate, that the immobilized
enzyme showed a strong transgalactosylation reaction, resulting in the formation of galactooligosaccharides (GalOS). The maximum
yield of GalOS of 34% was obtained when the degree of lactose conversion was roughly 80%. Hence, this immobilized enzyme can
be useful both for the cleavage of lactose at elevated temperatures, and the formation of GalOS, prebiotic sugars that have
a number of interesting properties for food applications. 相似文献
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