title: Relationship of inorganic pyrophosphatase and para-nitrophenylphosphatase activities of alkaline phosphatase in the microsomal fraction of isolated odontoblasts.
abstract: Some properties of inorganic pyrophosphatase (PPiase EC 3.6.1.1.) and para-nitrophenylphosphatase (p-NPPase EC 3.1.3.1) in the microsomal fraction of odontoblasts were investigated. The ratio of Mg2+:p-NPP and Mg2+:PPi for optimal enzyme activities was 1:1. A mutual substrate competition for PPiase and p-NPPase was described. In the presence of 0.1 mM EDTA, Mg2+ alone was not able to reactivate p-NPPase or PPiase. Instead, Zn2+ and Co2+ reactivated the PPiase, indicating they might act as cofactors for the enzyme. Mg2+ increased the PPiase activity, probably because Mg PP2-i was the true substrate for the enzyme. The diphosphonates ethane-1-hydroxy 1,1 diphosphonate (EHDP), methane diphosphonate (MDP) and dichloromethane diphosphonate (Cl2MDP) inhibited the PPiase activity.
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000378:metabolism*; D000469:Alkaline Phosphatase / Q000378:metabolism*; D000818:Animals; D004164:Diphosphonates / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008297:Male; D008861:Microsomes / Q000201:enzymology; D009804:Odontoblasts / Q000201:enzymology*; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D011755:Pyrophosphatases / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D004164:Diphosphonates; D004492:Edetic Acid; D000469:Alkaline Phosphatase; D010744:Phosphoric Monoester Hydrolases; D009597:4-Nitrophenylphosphatase; D011755:Pyrophosphatases