| 11750998 |
Jesus JB, Lopes AH, Meyer-Fernandes JR: Characterization of an ecto-ATPase of Tritrichomonas foetus. Vet Parasitol. 2002 Jan 3;103(1-2):29-42.
In this work, we describe the ability of living Tritrichomonas foetus to hydrolyze extracellular ATP. The addition of MgCl (2) to the assay medium increased the ecto-ATPase activity in a dose-dependent manner. At 5mM ATP, half maximal stimulation of ATP hydrolysis was obtained with 0.46mM MgCl (2). The ecto-ATPase activity was also stimulated by MnCl (2) and CaCl (2), but not by SrCl (2). The Mg (2+)-dependent ATPase presents two apparent K (m) values for Mg-ATP (2-) (K (m1)=0.03 mM and K (m2)=2.01 mM). ATP was the best substrate for this enzyme, although other nucleotides such as ITP, CTP, UTP also produced high reaction rates. GTP produced a low reaction rate and ADP was not a substrate for this enzyme. The Mg (2+)-dependent ecto-ATPase activity was insensitive to inhibitors of other ATPase and phosphatase activities, such as oligomycin, sodium azide, bafilomycin A (1), ouabain, furosemide, vanadate, molybdate, sodium fluoride and levamizole. The acid phosphatase inhibitors (vanadate and molybdate) inhibited about 60-70% of the Mg (2+)-independent ecto-ATPase activity, suggesting that the ATP hydrolysis measured in the absence of any metal divalent could, at least in part, also be catalyzed by an ecto-phosphatase present in this cell. In order to confirm the observed Mg (2+)-dependent activity as an ecto-ATPase, we used an impermeant inhibitor, 4,4'-diisothiocyanostylbene-2',2'-disulfonic acid (DIDS) as well as suramin, an antagonist of P (2) purinoreceptors and inhibitor of some ecto-ATPases. These two reagents inhibited the Mg (2+)-dependent ATPase activity in a dose-dependent manner. This ecto-ATPase was stimulated by more than 90% by 50mM D-galactose. Since previous results showed that D-galactose exposed on the surface of host cells is involved with T. foetus adhesion, the Mg (2+)-dependent ecto-ATPase may be involved with cellular adhesion and possible pathogenicity. |
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