원문정보
초록
영어
Glucose inhibition by β-galactosidase from Caldicellulosiruptor saccharolyticus is the lowest among the currently known β-galactosidases. However, the enzyme activity for lactose hydrolysis is inhibited at low galactose concentrations. In order to reduce galactose inhibition, the predicted galactose-binding residues, which were determined by sequence alignment, were replaced separately with Ala.
The activities of the Ala-substituted mutant enzymes were assessed with the addition of galactose. As a consequence, amino acid at position 349 was correlated with the reduction in galactose inhibition. The F349S mutant exhibited the highest activity in the presence of galactose relative to the activity measured in the absence of galactose among the tested mutant enzymes at position 349. The Ki of the F349S mutant, which was 13-fold that of the wild-type enzyme, was the highest among the reported values of β-galactosidases. The wild-type enzyme hydrolyzed 62% of 100 g lactose L−1 with the addition of 30 g galactose L−1, whereas the F349S mutant hydrolyzed more than 99%. This is, to the best of our knowledge, the first report regarding the reduction of product inhibition via the mutation of β-galactosidase.