Enzyme lactase

Enzymes are a specialized type of protein that act as biological catalysts for chemical reactions in living organisms. The action of enzymes is critical for life, providing energy, disposing of waste and allowing organisms to function.

Lactase (β-galactosidase) is a metalloenzyme exhibiting broad substrate specificity. It is the enzyme that hydrolyzes lactose to glucose and galactose. The activity of lactase is highly conserved through evolution, and derives from the β -galactosidase family of enzymes — a family present from Escherichia coli through to Homo sapiens.

In the human intestine, lactose is hydrolyzed by lactase into glucose and galactose. These components are then absorbed by the epithelial cells of the small intestine and transmitted to the blood stream.

Glucose and galactose are then used primarily for the generation of adenosine triphosphate (ATP) via the citric acid cycle and oxidative phosphorylation. During neonate and infant development, lactase is highly expressed in the human digestive system, breaking down lactose received from breast milk of which lactose is the primary carbohydrate component, and one of the key sources of nutrition during early years.

In lactose-intolerant individuals, hydrolysis of lactose alleviates symptoms of gastrointestinal disorders.

β-galactosidases are widespread in microorganisms, animals and plants. The enzyme lactase in humans and other mammals is ordinarily present only in the mucosal (epithelial) cells of the small intestine. It is located on the luminal side of the cell membrane of villi cells.

The molecular weight of lactase from different sources varies from 67-630 KD. β-galactosidase from E. coli is tetrameric, being composed of four identical subunits of 135 KD each with an independent active site. The optimum pH for the enzyme is 6-8.
Enzyme lactase