Studies on β-Galactosidase. I. Purification and Properties of β-Galactosidase I and II from Sclerotium tuliparum

抄録

Acid β-galactosidase I and II (β-D-galactoside galactohydrolase, EC 3. 2. 1. 23) from Sclerotium tuliparum were purified by column chromatography with DEAE-cellulose, SP-Sephadex C-50, Sephadex G-200 and by isoelectric focusing (pI, 4.5 and 4.4, respectively). The purified β-galactosidase I and II were homogeneous in disc electrophoresis. The enzymes were most active at pH 2.0 and stable over a pH range from 3.0 to 6.0 at 37° for 3 hr. Optimum temperatures of β-galactosidase I and II were 53° and 47°, respectively, and the thermal stability of β-galactosidase I was slightly higher than that of β-galactosidase II. Both enzymes were completely inactivated by N-bromosuccinimide at 0.01 mM. K_m of β-galactosidase I and II were 1.4 mM and 1.2 mM for o-nitrophenyl β-D-galactopyranoside (ONPG) and 20 mM and 19 mM for lactose, respectively, and V_max of β-galactosidase I and II were 433 μmoles·min^-1·mg^-1 and 480 μmoles·min^-1·mg^-1 for ONPG and 139 μmoles·min^-1·mg^-1 and 149 μmoles·min^-1·mg^-1 for lactose, respectively.