Convergent evolution of Trichomonas vaginalis lactate dehydrogenase from malate dehydrogenase

Lactate dehydrogenase (LDH) is present in the amitochondriate parasitic pro tist Trichomonas vaginalis and some but not ail other trichomonad species. The derived amino acid sequence of T. vaginalis LDH (TvLDH) was found to be more closely related to the cytosolic malate dehydrogenase (MDH) of the sa me species than to any other LDH. A key difference between the two T. vagin alis sequences was that Arg91 of MDH, known to be important in coordinating the C-4 carboxyl of oxalacetate/malate, was replaced by Leu91 in LDH. The change Leu91Arg by site-directed mutagenesis converted TvLDH into an MDH. T he reverse single amino acid change Arg91Leu in TvMDH, however, gave a prod uct with no measurable LDH activity. Phylogenetic reconstructions indicate that TvLDH arose from an MDH relatively recently.