Inhibitors: p-Chloromercuribenzoate, iodoacetamide, heavy metal ions (Zn²⁺, Fe²⁺, Zn²⁺, Cd²⁺, Cu²⁺, Pb²⁺, Ag⁺, Hg²⁺), ionic Detergents (SDS, DAC, etc.). Contaminants: The preparation is practically free from other glycosidases (a-galactosidase, a-,b-glucosidase, a-,b-mannosidase, etc.) and proteinase. Principle: o-Nitrophenyl-b-D-galactopyranoside (ONPG) b-galactosidase > o-Nitrophenol (ONP) + D-Galactose. The appearance of o-nitrophenol is measured at 410 nm by spectrophotemetry. Thermal Stability: Below 50 °C (pH 7,3; 15 min) (Lit.), Optimum Temperature: 50 to 55 °C (Lit.).

• Substrate specificity: specifically hydrolyses β-D-galactosyl linkage

One unit catalyses the hydrolysis of 1 µmole of o-nitrophenyl-β-D-galactopyranoside per minute at 25 °C, pH 7,5.

β-galactosidase cleaves lactose into its monosaccharide components, glucose and galactose. It also catalyses the transglycosylation of glucose into allolactose, the inducer of β-galactosidase, in a feedback loop.