IAP Background Information The intestinal alkaline phosphatase gene (ALPI) encodes a digestive brush-border enzyme, IAP (also designated ALP), which is highly upregulated during small intestinal epithelial cell differentiation. IAP, an enterocyte differentiation marker that functions to limit fat absorption, has been implicated in trans-cellular transport of chylomicrons and in chylomicron formation. At high pH, IAP removes phosphate groups from proteins and from the 5' end of DNA and RNA. Most mammals have four different IAP isozymes: placental, placental- like, intestinal and non tissue-specific. Non tissue-specific isozymes are found in liver, kidney and bone. Tissues with particularly high concentrations of IAP include the liver, bile ducts, placenta and bone. Damaged or diseased tissue releases enzymes into the blood, so serum IAP measurements can be abnormal in many conditions, including bone disease and liver disease. Serum IAP levels vary among ABO blood groups, and fatty acid metabolism may change among ABO blood types. Intestinal alkaline phosphatase is more prevalent in humans of blood group O or B.
