Possible regulation mechanism of potent nucleoside triphosphate hydrolase in Toxoplasma gondii.

A dormant enzyme, nucleoside triphosphate hydrolase (EC 3.6.1.3) purified from the tachyzoite of Toxoplasma gondii, was activated by the treatment with dithiothreitol. The catalytic activity remained after exclusion of dithiothreitol from the enzyme solution with a Sephadex G-25 column. This activity was completely blocked by the additional treatment with N-ethylmaleimide. It was concluded that the activation occurred through the reductive cleavage of disulfide bond on the enzyme. The reduced type of thioredoxin, partially purified from mouse liver, could replace the effect of dithiothreitol. These results strongly suggest that the enzyme activity is regulated by the oxido-reduction change in the enzyme molecule.