Biochemical characterization of an ecto-ATP diphosphohydrolase activity inCandida parapsilosis and its possible role in adenosine acquisition and pathogenesis

Abstract

In this work, we describe the ability of intact cells of Candida parapsilosis to hydrolyze extracellular ATP. ATP hydrolysis was stimulated by MgCl2 in a dosedependent manner. The ecto-ATPase activity was increased in the presence of 5 mM MgCl2, with values of Vmax and apparent Km for Mg-ATP2 increasing to 33.80 1.2 nmol Pi h1 108 cells and 0.6 0.06 mM, respectively. Inhibitors of phosphatases, mitochondrial Mg21-ATPases and Na1-ATPases had no effect on the C. parapsilosis Mg21-stimulated ATPase activity, but extracellular impermeant compounds, 4,40 -diisothiocyanatostilbene-2,20 disulfonic acid and suramin, reduced enzyme activity in yeast living cells by 83.1% and 81.9%, respectively. ARL 67156 (6-N,N0 -diethyl-D-b-g-dibromomethylene ATP), a nucleotide analogue, also inhibited the ecto-ATPase activity in a dose-dependent manner. ATP was the best substrate for the yeast Mg21-stimulated ecto-enzyme, but ADP, ITP, CTP, GTP and UTP were also hydrolyzed. A direct relationship between ecto-ATPase activity and adhesion to host cells was observed. In these assays, inhibition of enzyme activity resulted in decreased levels of yeast adhesion to epithelial cells. Based also on the differential expression of ecto-ATPase activities in the different isolates of C. parapsilosis, the possible role of this enzyme in fungal biology is discussed.