title: Characterization of an ecto-ATPase activity in Cryptococcus neoformans.
abstract: Cryptococcus neoformans is the causative agent of pulmonary cryptococcosis and cryptococcal meningoencephalitis, which are major clinical manifestations in immunosuppressed patients. In the present study, a surface ATPase (ecto-ATPase) was identified in C. neoformans yeast cells. Intact yeasts hydrolyzed adenosine-5'-triphosphate (ATP) at a rate of 29.36+/-3.36nmol Pi/hx10(8) cells. In the presence of 5 mM MgCl(2), this activity was enhanced around 70 times, and an apparent K(m) for Mg-ATP corresponding to 0.61mM was determined. Inhibitors of phosphatases, mitochondrial Mg(2+)-ATPases, V-ATPases, Na(+)-ATPases or P-ATPases had no effect on the cryptococcal ATPase, but extracellular impermeant compounds reduced enzyme activity in living cells. ATP was the best substrate for the cryptococcal ecto-enzyme, but it also efficiently hydrolyzed inosine 5'-triphosphate (ITP), cytidine 5'-triphosphate (CTP), guanosine 5'-triphosphate (GTP) and uridine-5'-triphosphate (UTP). In the presence of ATP, C. neoformans became less susceptible to the antifungal action of fluconazole. Our results are indicative of the occurrence of a C. neoformans ecto-ATPase that may have a role in fungal physiology.
authors.affiliation: Instituto de Bioquímica Médica, Universidade Federal do Rio de Janeiro, CCS, Bloco H, Cidade Universitária, Ilha do Fundão, 21541-590 Rio de Janeiro, RJ, Brazil.
authors.forename: Itallo Collopy
authors.initials: IC
authors.lastname: Junior
authors.forename: Marcio L
authors.initials: ML
authors.lastname: Rodrigues
authors.forename: Celuta S
authors.initials: CS
authors.lastname: Alviano
authors.forename: Luiz R
authors.initials: LR
authors.lastname: Travassos
authors.forename: José Roberto
authors.initials: JR
authors.lastname: Meyer-Fernandes
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000935:Antifungal Agents / Q000494:pharmacology; D002473:Cell Wall / Q000378:metabolism; D003455:Cryptococcus neoformans / Q000187:drug effects / Q000201:enzymology*; D003570:Cytidine Triphosphate / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015725:Fluconazole / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000378:metabolism; D007293:Inosine Triphosphate / Q000378:metabolism; D015636:Magnesium Chloride / Q000494:pharmacology; D014544:Uridine Triphosphate / Q000378:metabolism
chemical_list: D000935:Antifungal Agents; D015636:Magnesium Chloride; D007293:Inosine Triphosphate; D003570:Cytidine Triphosphate; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D015725:Fluconazole; D000251:Adenosine Triphosphatases; D014544:Uridine Triphosphate