Characterization of an ectonucleoside triphosphate diphosphohydrolase 1 activity in alkaline phosphatase-depleted rat osseous plate membranes: possible functional involvement in the calcification process.
An ectonucleoside triphosphate diphosphohydrolase 1 (NTPDase1) activity present in alkaline phosphatase-depleted rat osseous plate membranes, obtained 14 days after implantation of demineralized bone particles in the subcutaneous tissue of Wistar rats, was characterized. At pH 7.5, NTPDase1 hydrolyzed nucleotide triphosphates at rates 2.4-fold higher than those of nucleotide diphosphates, while the hydrolysis of nucleotide monophosphates and non-nucleotide phosphates was negligible. NTPDase 1 hydrolyzed ATP and ADP following Michaelis-Menten kinetics with V=1278.7+/-38.4 nmol Pi/min/mg and K(M)=83.3+/-2.5 microM and V=473.9+/-18.9 nmol Pi/min/mg and K(M)=150.6+/-6.0 microM, respectively, but in the absence of magnesium and calcium ions, ATP or ADP hydrolysis was negligible. The stimulation of the NTPDase1 by calcium (V=1084.7+/-32.5 nmol Pi/min/mg; and K(M)=377.8+/-11.3 microM) and magnesium (V=1367.2+/-41.0 nmol Pi/min/mg and K(M)=595.3+/-17.8 microM) ions suggested that each ion could replace the other during the catalytic cycle of the enzyme. Oligomycin, ouabain, bafilomycin A(1), theophylline, thapsigargin, ethacrynic acid, P(1),P(5)-(adenosine-5')-pentaphosphate and omeprazole had negligible effects on the hydrolysis of ATP and ADP by NTPDase1. However, suramin and sodium azide were effective inhibitors of ATP and ADP hydrolysis. To our knowledge this is the first report suggesting the presence of NTPDase1 in rat osseous plate membranes. Considering that the ectonucleoside triphosphate diphosphohydrolase family of enzymes participates in many regulatory functions, such as response to hormones, growth control, and cell differentiation, the present observations raise interesting questions about the participation of this activity in the calcification process.
Demenis
Marlene A
MA
Departamento de Química-Faculdade de Filosofia Ciências e Letras de Ribeirão Preto/USP, Avenida Bandeirantes 3.900, 14040-901 Ribeirão Preto, SP, Brazil.
Furriel
Rosa P M
RP
Leone
Francisco A
FA
D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000408:Alamethicin / Q000494:pharmacology; D000469:Alkaline Phosphatase / Q000172:deficiency; D000818:Animals; D015703:Antigens, CD; D001081:Apyrase / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D002113:Calcification, Physiologic; D002118:Calcium; D002384:Catalysis / Q000187:drug effects; D006132:Growth Plate / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D008274:Magnesium; D008566:Membranes / Q000201:enzymology; D051381:Rats; D013379:Substrate Specificity
D015703:Antigens, CD; D000408:Alamethicin; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000469:Alkaline Phosphatase; D001081:Apyrase; C067869:CD39 antigen; D008274:Magnesium; D002118:Calcium