A novel gene for lactate dehydrogenase was identified from the genomic sequence of Trichomonas vaginalis (TvLDH). The corresponding protein had a higher similarity to the malate dehydrogenase of the same species (TvMDH) than to any other LDH. We hypothesized that TvLDH arose from TvMDH by convergent evolution relatively recently . Comparative models were constructed for TvLDH and TvMDH to study the sequences in the structural context and to suggest site-directed mutagenesis experiments for elucidating specificity changes in this apparent case of convergent evolution of enzymatic specificity. The native and mutated enzymes were expressed and their activities were compared . The individual modeling steps of this study are described next.