Alpha-amylase 2B is a digestive enzyme that in humans is encoded by the AMY2B gene. This enzyme functions to break down carbohydrates, especially large carbohydrates like starch. This enzyme (along with AMY2A) is one of the primary alpha-amylases secreted by the acinar cells of the pancreas into pancreatic juice, which is released into the small intestines.
Function
Amylases are secreted proteins that hydrolyze 1,4-alpha-glucoside bonds in oligosaccharides and polysaccharides, and thus catalyze the first step in digestion of dietary starch and glycogen. The human genome has a cluster of several amylase genes that are expressed at high levels in either the salivary glands (AMY1A, AMY1B, AMY1C) or pancreas (AMY2A, AMY2B). This gene encodes an amylase isoenzyme produced by the pancreas. Similar to AMY1, the number of AMY2-encoding genes varies from individual to individual, however the proteins encoded by AMY2A and AMY2B are not identical (though they are ~99% similar).
Promotor region
AMY2B is distinct from AMY2A and the AMY1 genes by a difference in its promotor region. All AMY1 and AMY2 genes have a γ-actin pseudogene located in their promotor region. In all but AMY2B, this pseudogene is interrupted by a retroviral-like sequence. This may impact the regulation of these genes, and has been cited as evidence for the claim that the (salivary) AMY1 genes originated as copies of an AMY2 gene (see Amylase § Evolution).
