title: CrATP as a new inhibitor of ecto-ATPases of trypanosomatids.
abstract: Trypanosomatid protozoa include heteroxenic species some of them pathogenic for men, animals and plants. Parasite membrane contains ecto-enzymes whose active sites face the external medium rather than the cytoplasm. Herpetomonas sp. displayed a Mg2+-dependent ecto-ATPase activity, a Mg-independent ecto-ADPase and an ecto-phosphatase activity. Both, the ecto-ADPase and phosphatase activities were insensitive to CrATP (chromium(III) adenosine 5'-triphosphate complex). Ecto-ATPase activity was reversibly inhibited. At 2 mm ATP the apparent Ki was 4 x 7+/-1 x 0 microm but a fraction of about 40-50% was insensitive to CrATP. Remarkably, at low substrate concentration (0 x 2 mm) more than 90% of the ecto-ATPase was inhibited with Ki=0 x 33+/-0 x 10 microm. These parameter dependences are interpreted as the presence of 2 ecto-ATPases activities, one of them with high ATP apparent affinity and sensitivity to CrATP. DIDS (4,4 diisothiocyanatostilbene 2,2' disulfonic acid), suramin and ADP were also effective as inhibitors. Only ADP presented no additive inhibition with CrATP. The pattern of partial inhibition by CrATP was also observed for the ecto-ATPase activities of Leishmania amazonensis, Trypanosoma cruzi and Trypanosoma rangeli. CrATP emerges as a new inhibitor of ecto-ATPases and as a tool for a better understanding of properties and role of ecto-ATPases in the biology of parasites.
authors.affiliation: Instituto de Bioquímica Médica, Programa de Biologia Estrutural, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro Rio de Janeiro, Brasil.
authors.forename: O C
authors.initials: OC
authors.lastname: Moreira
authors.forename: P F
authors.initials: PF
authors.lastname: Rios
authors.forename: F F
authors.initials: FF
authors.lastname: Esteves
authors.forename: J R
authors.initials: JR
authors.lastname: Meyer-Fernandes
authors.forename: H
authors.initials: H
authors.lastname: Barrabin
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D013498:Suramin / Q000494:pharmacology; D013997:Time Factors; D014351:Trypanosomatina / Q000187:drug effects* / Q000201:enzymology*
chemical_list: D004791:Enzyme Inhibitors; D013498:Suramin; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid