title: Possible functions of alkaline phosphatase in dental mineralization: cadmium effects.
abstract: In mineralizing dental tissues the non-specific alkaline phosphatase, using paranitrophenylphosphate (p-NPP) as substrate, is also capable of splitting inorganic pyrophosphate (PPi). In contrast to the p-NPP-ase part of the enzyme, the PPi-ase part requires Zn2+ as a cofactor for its hydrolytic activity. The PPi-ase activity of the enzyme can be inhibited by cadmium ions (Cd2+), perhaps by replacing Zn2+ from the active site of the enzyme molecule. In addition to splitting PPi, the PPi-ase part of the enzyme may also be involved in the phosphorylation process of yet undetermined organic macromolecules. Cd2+ inhibits this phosphorylation process. Inhibition of the PPi-ase activity can also be accomplished by ascorbic acid known for its capacity to complex bivalent cations. Ascorbic acid may accordingly also remove Zn2+ from the active site of the PPi-ase. It is suggested that in developing dental tissues alkaline phosphatase is not only associated with the transport of phosphate ions towards the mineralization front, but is also involved in the phosphorylation of organic macromolecules, a process activated the PPi-ase part of the enzyme.
authors.affiliation: Dept. of Oral Cell Biology, ACTA, Vrije Universiteit, Amsterdam, The Netherlands.
authors.forename: J H
authors.initials: JH
authors.lastname: Wöltgens
authors.forename: D M
authors.initials: DM
authors.lastname: Lyaruu
authors.forename: T J
authors.initials: TJ
authors.lastname: Bervoets
mesh_terms: D000469:Alkaline Phosphatase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D001205:Ascorbic Acid / Q000378:metabolism; D002104:Cadmium / Q000494:pharmacology*; D006224:Cricetinae; D003771:Dental Papilla / Q000187:drug effects / Q000378:metabolism; D004658:Enamel Organ / Q000187:drug effects / Q000378:metabolism; D043564:Inorganic Pyrophosphatase; D008647:Mesocricetus; D009596:Nitrophenols / Q000378:metabolism; D009805:Odontogenesis / Q000187:drug effects* / Q000502:physiology; D009924:Organ Culture Techniques; D009943:Organophosphorus Compounds / Q000378:metabolism; D010758:Phosphorus / Q000037:antagonists & inhibitors / Q000378:metabolism; D010761:Phosphorus Radioisotopes; D010766:Phosphorylation / Q000187:drug effects; D011392:Proline / Q000037:antagonists & inhibitors / Q000378:metabolism; D011755:Pyrophosphatases / Q000494:pharmacology; D014074:Tooth Calcification / Q000187:drug effects* / Q000502:physiology; D014083:Tooth Germ / Q000187:drug effects* / Q000378:metabolism; D014316:Tritium
chemical_list: D009596:Nitrophenols; D009943:Organophosphorus Compounds; D010761:Phosphorus Radioisotopes; D002104:Cadmium; D014316:Tritium; D010758:Phosphorus; C008644:nitrophenylphosphate; D011392:Proline; D000469:Alkaline Phosphatase; D011755:Pyrophosphatases; D043564:Inorganic Pyrophosphatase; D001205:Ascorbic Acid