The metalloenzyme glyoxalase I (GlxI) converts hemimercaptal of cytotoxic methylglyoxal and glutathione to nontoxic S-D-lactoylglutathione. GlxI of Escherichia coli enzyme is maximally active with Ni2+. It has been reported that there is no substrate kinetic isotope effect for the Ni2+ substituted enzyme. Our goal with this study is to investigate the first step of the proposed mechanism of the enzyme for the kinetic isotope effect, using density functional theory approaches. The quantum mechanical crystal method is used to model the enzyme active site. All calculations were performed using the density functional, B3LYP. Geometrical structures of the stationary points along the reaction path, were optimized using 6-31+G(d) basis set for C, O, H and N atoms and lanl2dz for Ni and S atoms. The model of the active site of GlxI were constructed, based on the crystal structure of the native enzyme (Protein Data Bank entry 1f9z). The results show that there is no significant kinetic isotopic effect neither for H1 nor for H2 , in line with the experimental results.
