Alkaline phosphatases are membrane-bound ectoenzymes that hydrolyze monophosphate esters at a high pH (pH8―10). Human ALP is classified into 4 types - tissue-nonspecific, intestinal, placenta, and germ cell – of which the tissue-nonspecific type is ubiquitously expressed in many tissues, including liver, bone, and kidney, and is therefore referred to as the liver/bone/kidney (LBK) type. ALP is linked to the membrane via glycosylphosphatidylinositol (GPI) anchors by means of posttranslational modification.Tissue-nonspecific alkaline phosphatase (TNAP) is expressed on the cell membrane of hypertrophicchondrocytes, osteoblasts, and odontoblasts, and is also concentrated on the membranes of the matrix vesicles budding from these cells. TNAP hydrolyzes pyrophosphate and provides inorganicphosphate to promote mineralization. Inorganic pyrophosphate, pyridoxal phosphate, andphosphoethanolamine are thought to be the physiologic substrates of TNAP.Theseaccumulate in the event of TNAP deficiency, e.g., in cases of hypophosphatasia.[1]