On the properties of alpha-glucosidase and the binding of glucose to the enzyme.
An alpha-glucosidase was purified from baker's yeast. The molecular weight was approximately 44 000 daltons. SDS-disc gel electrophoresis suggested that the enzyme consisted of four subunits. The isoelectric point was at pH 5.4. The Km values for p-nitrophenyl alpha-D-glucopyranoside and maltose were 2.9 X 10(-4) and 2.5 X 10(-2) M, respectively. Binding of 2-(p-toluidino)naphthalene-6-sulfonate to the alpha-glucosidase was associated with a strong increase in fluorescence. The dissociation constant of the enzyme-TNS complex was 8 X 10(-5) M. The fluorescent probe did not interfere with the binding of glucose to the enzyme although the alpha-glucosidase was inhibited by high concentrations of TNS. The formation of an enzyme-glucose complex was indicated by an increase of fluorescence and by a shift in the wavelength for maximal emission which suggests that the binding process is associated with a change in conformation. The dissociation constant of the glucose--alpha-glucosidase complex KD = 0.57 X 10(-3) M, was calculated from the increase in fluorescence as a function of glucose concentration.
D005947:Glucose / Q000378:metabolism*; D005959:Glucosidases / Q000378:metabolism*; D009282:Naphthalenesulfonates / Q000378:metabolism; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D014052:Toluidines / Q000378:metabolism; D000520:alpha-Glucosidases / Q000302:isolation & purification / Q000378:metabolism*
D009282:Naphthalenesulfonates; D014052:Toluidines; D005959:Glucosidases; D000520:alpha-Glucosidases; D005947:Glucose