Cys126 is a completely conserved residue in triosephosphate isomerase that
is proximal to the active site but has been ascribed no specific role in catal-ysis. A previous study of the C126S and C126A mutants of yeast TIM
reported substantial catalytic activity for the mutant enzymes, leading to
the suggestion that this residue is implicated in folding and stability [Gonz-alez-Mondragon Eet al.
The active site of triosephosphate isomerase (TIM, EC: 188.8.131.52), a
dimeric enzyme, lies very close to the subunit interface. Attempts to
engineer monomeric enzymes have yielded well-folded proteins with dra-matically reduced activity.
The synthesis of ATP in the human parasiteEntamoeba histolyticais car-ried out solely by the glycolytic pathway. Little kinetic and structural infor-mation is available for most of the pathway enzymes.
Plasmodium falciparumtriosephosphate isomerase (PfTIM)
contains two tryptophan residues, W11 and W168. One is
positioned in the interior of the protein, and the other is
located on the active-site loop 6. Two single-tryptophan
mutants, W11F and W168F, were constructed to evaluate
the contributions of each chromophore to the fluorescence
of the wild-type (wt) protein and to probe the utility of the
residues as spectroscopic reporters.