Identification and role of thiols in Toxoplasma gondii egress

The nucleoside triphosphate hydrolase of Toxoplasma gondii is a potent apyr ase that is secreted into the parasitophorous vacuole where it appears to b e essentially inactive in an oxidized form. Recent evidence shows that nucl eoside triphosphate hydrolase can be activated by dithiothreitol in vivo. O n reduction of the enzyme, there is a rapid depletion of host cell ATP. Pre vious results also demonstrate a dithiothreitol induced egress of parasites from the host cell with a concurrent Ca2+ flux, postulated to be a consequ ence of the release of ATP-dependent Ca2+ stores within the tubulovesicular network of the parasitophorous vacuole, Reduction of the nucleoside tripho sphate hydrolase appears crucial for its activation; however, the exact mec hanism of reduction/activation has not been determined. Using a variety of techniques, we slow here that glutathione promoters activate a Ca2+ flux an d decrease ATP levels in infected human fibroblasts, We further show the in vitro activation of nucleoside triphosphate hydrolase by endogenous reduci ng agents, one of which we postulate might be secreted into the PV by T. go ndii. Our findings suggest that the reduction of the parasite nucleoside tr iphosphate hydrolase, and ultimately parasite egress, is under the control of the parasites themselves.