title: In vivo measurement of dihydrofolate reductase and its inhibition by antifolates.
abstract: The ability of the enzyme dihydrofolate reductase to catalyze the formation of tetrahydrobiopterin from dihydrobiopterin was used to develop a method for measuring the activity of this enzyme in vivo. This method can be used to determine the activity of the enzyme in tissues as well as the extent and duration of inhibition of the enzyme by antifolates. Sepiapterin, which is converted to dihydrobiopterin by the enzyme sepiapterin reductase, was as effective a precursor as dihydrobiopterin and has been used in these studies because of its greater stability relative to dihydrobiopterin. Assay conditions must be established for each tissue and enzyme activity can be determined either by measuring the rate of disappearance of dihydrobiopterin or the rate of formation of tetrahydrobiopterin.
authors.affiliation: Department of Medicinal Biochemistry, Wellcome Research Laboratories, Research Triangle Park, North Carolina 27709.
authors.forename: S W
authors.initials: SW
authors.lastname: Bowers
authors.forename: D S
authors.initials: DS
authors.lastname: Duch
mesh_terms: D000818:Animals; D001708:Biopterins / Q000031:analogs & derivatives / Q000096:biosynthesis / Q000378:metabolism; D001921:Brain / Q000201:enzymology; D005493:Folic Acid Antagonists / Q000494:pharmacology*; D007276:Injections, Intraventricular; D008099:Liver / Q000201:enzymology; D008297:Male; D008727:Methotrexate / Q000494:pharmacology; D051379:Mice; D011621:Pteridines / Q000008:administration & dosage / Q000378:metabolism; D011622:Pterins; D011743:Pyrimidines / Q000494:pharmacology; D051381:Rats; D013762:Tetrahydrofolate Dehydrogenase / Q000378:metabolism*
chemical_list: D005493:Folic Acid Antagonists; D011621:Pteridines; D011622:Pterins; D011743:Pyrimidines; D001708:Biopterins; C017226:7,8-dihydrobiopterin; C016727:sepiapterin; D013762:Tetrahydrofolate Dehydrogenase; C003402:sapropterin; C024530:piritrexim; D008727:Methotrexate