Glycolate oxidase, an
FMN-dependent peroxisomal
oxidase, plays an important role in plants, related to photorespiration, and in animals, where it can contribute to the production of
oxalate with formation of
kidney stones. The best studied plant
glycolate oxidase is that of spinach; it has been expressed as a recombinant
enzyme, and its crystal structure is known. With respect to animals, the
enzyme purified from pig liver has been characterized in detail in terms of activity and inhibition, the
enzyme from human liver in less detail. We describe here the purification and initial characterization of the recombinant human
glycolate oxidase. Its substrate specificity and the inhibitory effects of a number of
anions are in agreement with the properties expected from previous work on
glycolate oxidases from diverse sources. The recombinant
enzyme presents an inhibition by excess
glycolate and by excess DCIP, which has not been documented before. These inhibitions suggest that
glycolate binds to the active site of the reduced
enzyme, and that DCIP also has affinity for the oxidized
enzyme.
Glycolate oxidase belongs to a family of l-2-hydroxy-acid-oxidizing flavoenzymes, with strongly conserved active-site residues. A comparison of some of the present results with studies dealing with other family members suggests that residues outside the active site influence the binding of a number of
ligands, in particular
sulfite.