Glyoxalase I (GlxI) is one of the enzymes that shows a high metal dependency in its catalytic activity. For the catalytic activity, GlxI requires divalent metal ions (Zn(II), Ni(II), Co(II), or other metal ions, depending on the organism). It has been suggested that the metal specificity is related to the amino-acid sequence and the length of the enzyme. For example, Zn(II)-active GlxIs comprise additional short regions that are missing in the Zn(II)-inactive ones. Despite all studies of the reaction mechanism of GlxI, the metal preference of this enzyme has not gained much attention. In this study, we have used the QM/MM method to study the metal preference of GlxI from humans (HuGlxI) and corn (ZmGlxI), prototypes of Zn(II)-active and Zn(II)-inactive GlxIs, respectively. This enzyme can act upon a mixture of methylglyoxal (MG), glutathione (H-SG), and hemithioacetal (HTA). Depending on the number of substrates, there could be two mechanisms for the reaction of GlxI (single- and two-substrate mechanisms). We studied energy profiles for the two- and single-substrate mechanisms of HuGlxI and ZmGlxI with the Zn(II), Ni(II), and Co(II) ions. Our results show that the Zn ion gives the lowest barrier for the two- and single-substrate reaction mechanism of HuGlxI. This agrees with the experimental observation that HuGlxI is most active with Zn. However, the barriers diverge from the experimental results for ZmGlxI.
