Giardia lamblia: Biochemical characterization of an ecto-ATPase activity

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 × h −1 × 10 −6 cells). The ATP hydrolysis was stimulated by MgCl 2 in a dose-depende...

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Bibliographic Details
Published in:	Experimental parasitology Vol. 119; no. 2; pp. 279 - 284
Main Authors:	Pinheiro, Ana Acacia de Sá, Cosentino-Gomes, Daniela, Lanfredi-Rangel, Adriana, Ferraro, Rodrigo Barbosa, Souza, Wanderley De, Meyer-Fernandes, José Roberto
Format:	Journal Article
Language:	English
Published:	San Diego, CA Elsevier Inc 01-06-2008 Elsevier
Subjects:	4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid - pharmacology Adenosine Triphosphatases - antagonists & inhibitors Adenosine Triphosphatases - metabolism Adenosine Triphosphate - metabolism Animals Biological and medical sciences Chromatography, High Pressure Liquid - methods Dose-Response Relationship, Drug Ecto-ATPase ENTPase Fundamental and applied biological sciences. Psychology Giardia lamblia Giardia lamblia - enzymology Hydrogen-Ion Concentration Hydrolysis Life cycle. Host-agent relationship. Pathogenesis Magnesium Chloride - pharmacology Protozoa Purine Nucleotides - metabolism Substrate Specificity Suramin - pharmacology Time Factors Giardia lamblia Ecto-ATPase ENTPase Protozoa Parasite Activity Diplomonadida
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Summary:	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 × h −1 × 10 −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.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0014-4894 1090-2449
DOI:	10.1016/j.exppara.2008.02.006