| 15652174 |
Leal DB, Streher CA, Neu TN, Bittencourt FP, Leal CA, da Silva JE, Morsch VM, Schetinger MR: Characterization of NTPDase (NTPDase1; ecto-apyrase; ecto-diphosphohydrolase; CD39; EC 3.6.1.5) activity in human lymphocytes. Biochim Biophys Acta. 2005 Jan 18;1721(1-3):9-15. Epub 2004 Oct 6.
Human lymphocytes contain NTPDase (NTPDase-1; ecto-apyrase; ecto-diphosphohydrolase; CD39; EC 3.6.1.5), a cation-dependent enzyme that hydrolyzes ATP and ADP and also other di- and triphosphate nucleosides, acting at an optimum pH of 8.0. A significant inhibition of ATP and ADP hydrolysis (P <0.05) was observed in the presence of 20 mM sodium azide. NTPDase inhibitors, 20 mM sodium fluoride, 0.2 mM trifluoperazine and 0.3 mM suramin, significantly decreased ATP and ADP hydrolysis (P <0.05) and ADP hydrolysis was only inhibited by 0.5 mM orthovanadate (P <0.05). ATP and ADP hydrolysis was not inhibited in the presence of 0.01 mM Ap5A (P1,P5-di (adenosine-5') pentaphosphate), 0.1 mM ouabain, 1 mM levamisole, 2 microg/mL oligomycin, 0.1 mM N-ethylmaleimide (NEM), or 5 mM sodium azide. With respect to kinetic behavior, apparent K (m) values of 77.6+/-10.2 and 106.8+/-21.0 microM, and V (max) values of 68.9+/-8.1 and 99.4+/-8.5 (mean+/-S.E., n=3) nmol Pi/min/mg protein were obtained for ATP and ADP, respectively. A Chevilard plot demonstrated that only one enzymatic site is responsible for the hydrolysis of ATP and ADP. The presence of CD39 was determined by flow cytometry, showing a low density of 2.72+/-0.24% (mean+/-S.E.; n=30) in human peripheral lymphocytes. The study of NTPDase activity in human lymphocytes may be important to determine the immune response status against infectious agents related to ATP and ADP hydrolysis. |
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