GLO1 - Properties

Properties

Glyoxalase I requires bound metal ions for catalysis. The human enzyme and its counterparts in yeast (Saccharomyces cerevisiae) and Pseudomonas putida use divalent zinc, Zn2+. By contrast, the prokaryotic versions often use a nickel ion. Interestingly, the glyoxalase I found in eukaryotic trypanosomal parasites such as Leishmania major and Trypanosoma cruzi can also use nickel for activity, possibly reflecting an acquisition of their GLO1 gene by horizontal gene transfer.

A striking property of glyoxalase I is its lack of specificity for the catalytic metal ion. Most enzymes prefer to bind one particular type of metal, and their catalytic activity depends on having bound that metal. For example, oxidoreductases often use a specific metal ion such as iron, manganese or copper and will fail to function if their preferred metal ion is replaced, due to differences in the redox potential; thus, the ferrous superoxide dismutase cannot function if its catalytic iron is replaced by manganese, and vice versa. By contrast, although human glyoxalase I prefers to use divalent zinc, it is able to function with many other divalent metals, including magnesium, manganese, cobalt, nickel and even calcium.; however, the enzyme is inactive with the ferrous cation. Similarly, although the prokaryotic glyoxalase I prefers nickel, it is able to function with cobalt, manganese and cadmium; however, the enzyme is inert with bound zinc, due to a change in coordination geometry from octahedral to trigonal bipyramidal. Structural and computational studies have revealed that the metal binds the two carbonyl oxygens of the methylglyoxal moiety at two of its coordination sites, stabilizing the enediolate anion intermediate.

Another unusual property of glyoxalase I is its inconsistent stereospecificity. The first step of its reaction mechanism (the abstraction of the proton from C₁ and subsequent protonation of O₂) is not sterospecific, and works equally well regardless of the initial chirality at C₁ in the hemithioacetal substrate. The resulting enediolate intermediate is achiral, but the second step of the reaction mechanism (the abstraction of a proton from O₁ and subsequent protonation of C₂) is definitely stereospecific, producing only the (S) form of D-lactoylglutathione. This is believed to result from the two glutamates bound oppositely on the metal ion; either one is able to carry out the first step, but only one is able to carry out the second step. The reason from this asymmetry is not yet fully determined.