All isolates presented ADA activity, although we could not establish a relationship between isolate source and activity (Table S2). Herein, we described the biochemical properties of an ADA activity and two ADA-related sequences present on intact trophozoites of T. vaginalis. Cellular integrity was assessed, before and after the reactions, and the viability of the trophozoites was not affected by any of the conditions used in the assays. The influence of pH on the adenosine deamination in T. vaginalis was verified and the results demonstrated that the optimal pH for ADA activity reached at Apoptosis inhibitor 7.5. It is known that vaginal pH in noninfected women is approximately 4.3, but can vary from
below 4 to pH 7.5 during the menstrual cycle (Stevens-Simon et al., 1994). In agreement, previous studies demonstrated that the optimal pH values for ADA activities from the camel tick, H. dromedarii,
and from the trematode F. gigantica were also 7.5 (Mohamed, 2006; Ali, 2008). Cation exposures (2.5 mM) were able to decrease the adenosine deamination in T. vaginalis in approximately 50%. Higher concentration of calcium (5.0 mM) completely abolished the enzyme activity and the presence of EDTA, a chelating agent, restored ADA activity. BAY 80-6946 Previous data showed that zinc and other divalent cations are able to interact with other amino acid residues and induce an inhibition of the enzyme activity (Cooper et al., 1997; Mohamed, 2006; Rosemberg et al., 2008). Because zinc is toxic to tetracosactide T. vaginalis, we could not perform the experiments on the influence of this metal in ADA activity in intact trophozoites (Langley et al., 1987; Houang et al., 1997). Additional
studies are necessary to explain the relevance of the inhibition of ADA activity by calcium and magnesium in T. vaginalis physiology, because magnesium is the most abundant divalent cation in living cells, with a total cellular concentration between 14 and 20 mM (Schmitz et al., 2007). The substrate curve demonstrated that the apparent KM for adenosine was around 1.13 ± 0.07 mM and the estimated Vmax for adenosine deamination was 2.61 ± 0.054 NH3 min−1 mg−1 protein in T. vaginalis. The kinetic data obtained in this study are in accordance with other studies related to ADA activity, although there are some variations of KM among different ADA members. The KM value of H. dromedarii ADA2 was estimated to 0.5 mM adenosine (Mohamed, 2006), which is relatively close to several ADAs from different sources, such as rat brain (0.45 mM) (Centelles et al., 1988), bovine brain (0.4 mM) (Lupidi et al., 1992), human (0.46 mM) and chicken liver (0.33 mM) (Iwaki-Egawa & Watanabe, 2002). However, lower KM values were reported for ADA activity from mice intestine (0.023 mM) (Singh & Sharma, 2000) and from the sand fly Lutzomyia longipalpis (0.01 mM) (Charlab et al., 2000). Additional data on biochemical characterization revealed the strong preference of the T.