title: New pteridine substrates for dihydropteridine reductase and horseradish peroxidase.
abstract: The oxidation of 4,5-diaminopyrimidin-6(1H)-one, 5,6,7,8-tetrahydropteridin-4(3H)-one, its 6-methyl and cis-6,7-dimethyl derivatives, and 6-methyl- and cis-6-7-dimethyl-5,6,7,8-tetrahydropterins, by horseradish peroxidase/H2O2 is enzymic and follows Michaelis-Menten kinetics, and its Km and kcat. values were determined. This oxidation of 5,6,7,8-tetrahydropterins produces quinonoid dihydropterins of established structure, and they are known to be specific substrates for dihydropteridine reductase. By analogy the peroxidase/H2O2 oxidation of the 5,6,7,8-tetrahydropteridin-4(3H)-ones should produce similar quinonoid dihydro species. The quinonoid species derived from 5,6,7,8-tetrahydropteridin-4(3H)-one and its 6-methyl and cis-6,7-dimethyl derivatives are shown to be viable substrates for human brain dihydropteridine reductase, and apparent Km and Vmax. values are reported.
mesh_terms: D001921:Brain / Q000201:enzymology; D004093:Dihydropteridine Reductase / Q000378:metabolism*; D006735:Horseradish Peroxidase / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism*; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000378:metabolism*; D011621:Pteridines / Q000378:metabolism*; D011622:Pterins / Q000378:metabolism; D011743:Pyrimidines / Q000378:metabolism; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
chemical_list: D011621:Pteridines; D011622:Pterins; D011743:Pyrimidines; D006735:Horseradish Peroxidase; D010544:Peroxidases; D004093:Dihydropteridine Reductase; D009247:NADH, NADPH Oxidoreductases; C030986:pyrimidine