Alkaline phosphatase, tissue-nonspecific isozyme (TNAP) (TNAP)

Bone-specific alkaline phosphatase (BAP) is a glycoprotein isoform of the enzyme tissue-nonspecific alkaline phosphatase (TNAP), which is encoded by the ALPL gene and primarily expressed on the surface of osteoblasts [8, 12]. It plays a fundamental role in skeletal mineralization by hydrolyzing inorganic pyrophosphate (PPi), a potent inhibitor of hydroxyapatite crystal formation, into inorganic phosphate [1, 18]. This enzymatic activity facilitates the deposition of mineral into the bone matrix and is essential for maintaining bone density and strength [2, 20]. Clinically, BAP serves as a sensitive biomarker for bone formation and turnover, used to monitor metabolic bone diseases such as osteoporosis, Paget's disease, and osteomalacia [5, 8]. Mutations in the ALPL gene lead to hypophosphatasia (HPP), a rare genetic disorder characterized by defective mineralization of bones and teeth [4, 16]. The primary therapeutic intervention targeting this pathway is asfotase alfa, a recombinant enzyme replacement therapy that restores TNAP activity in patients with HPP [1, 7]. Additionally, certain drugs like bisphosphonates can indirectly affect BAP activity through the chelation of essential metal cofactors like zinc and magnesium [17, 21].

Other names

Bone-specific alkaline phosphataseBAPBALPBSAPSkeletal alkaline phosphataseTissue-nonspecific alkaline phosphataseTNSALPALPL

Enzyme replacement therapy to restore catalytic activity and hydrolyze mineralization inhibitors like inorganic pyrophosphate [1, 16]; inhibition of catalytic activity by small molecules or chelation of metal cofactors [14, 17].