_ When someone is lactose intolerant, this means that the person has difficulty digesting the milk sugar lactose. Lactase, a beta-galactosidase found in the surface membrane of small-intestinal epithelial cells, is known as the enzyme that splits the milk sugar lactose to make more simple sugars like glucose and galactose (As seen clearly in the picture to the right). Lactase is mainly known as a digestive enzyme which is produced by specialized cells that usually line the lumen of the small intestine. These specialized cells absorb nutrients within the digestive tract of a person. The gene which is known to be responsible for guiding the production of the enzyme of lactase is called the LCT gene and can be found on chromosome 21. If this gene were to be damaged in any way shape or form, it would produce an improper production, as well as improper function of the enzyme.
The 4-fold internal homology which the genes hold leads to the idea that they evolved by two cycles of partial gene duplication. The repetition also suggests that the pro portion has come to be quite similar with the mature LPH, only the pro being water-soluble beta-glycosidase along with an additional cellular location. a-helices and B-sheets, and formation of disulfide bonds or other covalent interactions are functioning to stabilize and control particular regions of the protein. β-galactosidase (lactase) is a tetramer, stating that it has four subunits. This is an example of an enzyme which consists of a quaternary structure.