title: Giardia lamblia: biochemical characterization of an ecto-ATPase activity.
abstract: In this work, we describe the ability of living trophozoites of Giardia lamblia to hydrolyze extracellular ATP. In the absence of any divalent cations, a low level of ATP hydrolysis was observed (0.78+/-0.08 nmol Pi x h(-1)x10(-6) cells). The ATP hydrolysis was stimulated by MgCl(2) in a dose-dependent manner. Half maximum stimulation of ATP hydrolysis was obtained with 0.53+/-0.07 mM. ATP was the best substrate for this enzyme. The apparent K(m) for ATP was 0.21+/-0.04 mM. In the pH range from 5.6 to 8.4, in which cells were viable, this activity was not modified. The Mg(2+)-stimulated ATPase activity was insensitive to inhibitors of intracellular ATPases such as vanadate (P-ATPases), bafilomycin A(1) (V-ATPases), and oligomycin (F-ATPases). Inhibitors of acid phosphatases (molybdate, vanadate and fluoride) or alkaline phosphatases (levamizole) had no effect on the ecto-ATPase activity. The impermeant agent DIDS and suramin, an antagonist of P2 purinoreceptors and inhibitor of some ecto-ATPases, decreased the enzymatic activity in a dose-dependent manner, confirming the external localization of this enzyme. Besides ATP, trophozoites were also able to hydrolyse ADP and 5 AMP, but the hydrolysis of these nucleotides was not stimulated by MgCl(2). Our results are indicative of the occurrence of a G. lamblia ecto-ATPase activity that may have a role in parasite physiology.
authors.affiliation: Instituto de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Cidade Universitária, Ilha do Fundão, 21941-590, Rio de Janeiro, RJ, Brazil.
authors.forename: Ana Acacia
authors.initials: AA
authors.lastname: de Sá Pinheiro
authors.forename: Daniela
authors.initials: D
authors.lastname: Cosentino-Gomes
authors.forename: Adriana
authors.initials: A
authors.lastname: Lanfredi-Rangel
authors.forename: Rodrigo Barbosa
authors.initials: RB
authors.lastname: Ferraro
authors.forename: Wanderley
authors.initials: W
authors.lastname: De Souza
authors.forename: José Roberto
authors.initials: JR
authors.lastname: Meyer-Fernandes
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D004305:Dose-Response Relationship, Drug; D016829:Giardia lamblia / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D015636:Magnesium Chloride / Q000494:pharmacology; D011685:Purine Nucleotides / Q000378:metabolism; D013379:Substrate Specificity; D013498:Suramin / Q000494:pharmacology; D013997:Time Factors
chemical_list: D011685:Purine Nucleotides; D015636:Magnesium Chloride; D013498:Suramin; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; C027201:ectoATPase; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid