Lactase

Lactase (β‑galactosidase, EC 3.2.1.23) is a glycoside‑hydrolyzing enzyme that catalyzes the hydrolysis of the disaccharide lactose into its constituent monosaccharides, glucose and galactose. In humans, the enzyme is produced primarily by enterocytes of the small‑intestinal brush‑border, and its principal physiological role is to enable the absorption of dietary lactose from milk and dairy products.

• Lactase is a glycoside hydrolase belonging to the GH2 family.
• The human enzyme is a monomeric protein of 1,927 amino acids (~193 kDa) with the systematic IUPAC name “(β‑D‑galactopyranosyl‑(1→4)‑D‑glucoside) lactase”.
• Its primary structural features include a TIM‑barrel (β/α)8 catalytic domain, a C‑terminal β‑sandwich domain, and a calcium‑binding site that stabilizes the enzyme’s conformation.
• The active site contains three key residues: Glu374 (catalytic acid/base), Asp245 (stabilizes transition state), and a calcium ion that maintains structural integrity.
• The enzyme’s optimum pH is 6.5–7.0, and it is stable up to 40 °C; commercial preparations are often freeze‑dried to preserve activity and are standardized in International Units based on the hydrolysis of 1 µmol lactose per minute under assay conditions (pH 6.0, 37 °C).

• Commercial lactase is most commonly produced via recombinant DNA technology using Aspergillus niger or Kluyveromyces lactis expression systems, which yield high‑purity extracellular enzyme that can be harvested from fermentation broth.
• After fermentation, the enzyme is concentrated, purified (often by ultrafiltration and chromatography), and spray‑dried with carriers such as maltodextrin.
• In some “natural” products, lactase is extracted from bovine or goat intestinal mucosa, but this method is limited by low yield and potential allergenicity.
• Quality considerations include enzyme activity per unit weight (IU/g), stability under gastric pH (often protected by enteric coating), and absence of microbial contaminants.
• GMP‑certified manufacturers must test for heavy metals, mycotoxins, and residual DNA to meet regulatory standards (e.g., FDA, EFSA).