Inhibitory effects of anions and active site amino acid sequence of chicken liver L-2-hydroxyacid oxidase A, a member of the FMN-dependent alpha-hydroxyacid oxidizing enzyme family

Gene expression and activity of methionine converting enzymes in broiler chickens fed methionine isomers or precursors

Common dietary supplemental methionine (Met) sources include DL-methionine (DL-Met) and the Met precursor DL-2-hydroxy-4-(methylthio) butanoic acid (DL-HMTBA). For bio-utilization, D-Met and DL-HMTBA are converted into L-Met through oxidation and transamination. The objective of this study was to determine the effect of different dietary supplemental Met sources on gene expression and enzyme activity of Met oxidases in male broiler chickens. Liver, muscle, duodenum, jejunum, and ileum were collected at days 10 (d 10), 21 (d 21), and 26 (d 26) post-hatch from male broiler chickens that were fed a basal diet deficient in sulfur amino acids (SAA) (control), or the control diet supplemented with DL-Met, L-Met, or DL-HMTBA to meet SAA requirements. The mRNA abundance of D-Met oxidase, L-HMTBA oxidase, and D-HMTBA oxidase was measured by real-time PCR, and oxidase activities were measured using colorimetric assays (n = 5). Liver expressed more D- and L-HMTBA oxidase mRNA, while breast muscle and liver expressed more D-Met oxidase mRNA than other tissues. In the liver, DL-HMTBA and L-Met supplementation were associated with greater mRNA abundance of L-HMTBA oxidase compared to the control diet-fed group at d 10 but not d 21 or d 26. DL-HMTBA supplementation, however, was not associated with changes in the mRNA abundance of D-HMTBA oxidase. The Met-deficient diet at d 26 was associated with greater hepatic abundance of DAO mRNA, which is responsible for oxidation of amino acids. Oxidase activities were similar among the Met deficient and Met-supplemented groups. In conclusion, dietary Met supplementation influenced the transcriptional regulation and activity of Met oxidases in a tissue and age-specific manner. Met oxidases may thus act as a determining factor in the bioefficacy of different dietary supplemental Met sources.

Purification and characterization of recombinant human liver glycolate oxidase

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.