β-Galactosidase [EC 3.2.1.23] has been purified from a culture of Aspergillus oryzae by 2-propanol fractionation, column chromatography on DEAE-Sephadex A-50 and Sephadex G-200. The preparation was homogeneous on ultracentrifugation and disc electrophoresis.
The enzyme showed pH optima of 4.5 with ONPG¹ as a substrate and 4.8 with lactose as a substrate. The stable pH range was from 4.0 to 9.0 and the optimum temperature was 46°.
The Michaelis constants were 7.2×10^-4M with ONPG and 1.8×10^-2M with lactose. Hg²⁺, Cu²⁺, N-bromosuccinimide, and sodium laurylsulfate caused marked inhibition.
The apparent molecular weight was calculated to be about 105, 000 by Sephadex gel filtration and sucrose density gradient centrifugation.