title: Characterisation of an ATP diphosphohydrolase (Apyrase, EC 3.6.1.5) activity in Trichomonas vaginalis.
abstract: In the present report the enzymatic properties of an ATP diphosphohydrolase (apyrase, EC 3.6.1.5) in Trichomonas vaginalis were determined. The enzyme hydrolyses purine and pyrimidine nucleoside 5'-di- and 5'-triphosphates in an optimum pH range of 6.0--8.0. It is Ca(2+)-dependent and is insensitive to classical ATPase inhibitors, such as ouabain (1 mM), N-ethylmaleimide (0.1 mM), orthovanadate (0.1 mM) and sodium azide (5 mM). A significant inhibition of ADP hydrolysis (37%) was observed in the presence of 20 mM sodium azide, an inhibitor of ATP diphosphohydrolase. Levamisole, a specific inhibitor of alkaline phosphatase, and P(1), P(5)-di (adenosine 5'-) pentaphosphate, a specific inhibitor of adenylate kinase, did not inhibit the enzyme activity. The enzyme has apparent K(m) (Michaelis Constant) values of 49.2+/-2.8 and 49.9+/-10.4 microM and V(max) (maximum velocity) values of 49.4+/-7.1 and 48.3+/-6.9 nmol of inorganic phosphate x min(-1) x mg of protein(-1) for ATP and ADP, respectively. The parallel behaviour of ATPase and ADPase activities and the competition plot suggest that ATP and ADP hydrolysis occur at the same active site. The presence of an ATP diphosphohydrolase activity in T. vaginalis may be important for the modulation of nucleotide concentration in the extracellular space, protecting the parasite from the cytolytic effects of the nucleotides, mainly ATP.
authors.affiliation: Laboratório de Pesquisa Bioquímica, Departamento de Ciências Fisiológicas, Faculdade de Biociências, Pontifícia Universidade Católica do Rio Grande do Sul, Avenida Ipiranga, 6681, Caixa Postal 1429, 90619-900, Porto Alegre, RS, Brazil.
authors.forename: J A
authors.initials: JA
authors.lastname: de Aguiar Matos
authors.forename: F P
authors.initials: FP
authors.lastname: Borges
authors.forename: T
authors.initials: T
authors.lastname: Tasca
authors.forename: M R
authors.initials: MR
authors.lastname: Bogo
authors.forename: G A
authors.initials: GA
authors.lastname: De Carli
authors.forename: M
authors.initials: M
authors.lastname: da Graça Fauth
authors.forename: R D
authors.initials: RD
authors.lastname: Dias
authors.forename: C D
authors.initials: CD
authors.lastname: Bonan
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001081:Apyrase / Q000378:metabolism*; D002122:Calcium Chloride / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015636:Magnesium Chloride / Q000378:metabolism; D013379:Substrate Specificity; D014246:Trichomonas vaginalis / Q000201:enzymology*
chemical_list: D004791:Enzyme Inhibitors; D015636:Magnesium Chloride; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D001081:Apyrase; D002122:Calcium Chloride