where is lactase found in the human body
Lactase Lactase is an enzyme produced by many organisms. It is located in the brush border of the small intestine of humans and other mammals. Lactase is essential to the complete digestion of whole milk; it breaks down lactose, a sugar which gives milk its sweetness. Lacking lactase, a person consuming dairy products may experience the symptoms of lactose intolerance.[1] Lactase can be purchased as a food supplement, and is added to milk to produce "lactose-free" milk products.
Lac repressor The lac repressor (LacI) operates by a helix-turn-helix motif in its DNA binding domain binding base-specifically to the major groove of the operator region of the lac operon, with base contacts also made by residues of symmetry-related alpha helices, the "hinge" helices, which bind deeply in the minor groove.[1] This DNA binding causes the specific affinity of RNA polymerase for the promoter sequence to increase sufficiently that it cannot escape the promoter region and enter elongation, and so prevents transcription of the mRNA coding for the Lac proteins.[2] When lactose is present, allolactose binds to the lac repressor, causing an allosteric change in its shape. In its changed state, the lac repressor is unable to bind tightly to its cognate operator. This effect is referred to as induction, because it induces, rather than represses, expression of the metabolic genes. In vitro, Isopropyl β-D-1-thiogalactopyranoside (IPTG) is a commonly used allolactose mimic which can be used to induce transcription of genes being regulated by lac repressor.