title: The antithyroid agent 6-n-propyl-2-thiouracil is a mechanism-based inactivator of the neuronal nitric oxide synthase isoform.
abstract: 6-n-Propyl-2-thiouracil (6-PTU), the antithyroid agent, produces a time-, concentration-, and turnover-dependent inactivation of the NO synthetic capability of the neuronal nitric oxide synthase isoform irreversible by either arginine or (6R)-5,6,7,8-tetrahydro-L-biopterin. By contrast 6-PTU produces an inhibition of the cytokine-inducible and endothelial nitric oxide synthases fully reversible by arginine. The inactivation of neuronal nitric oxide synthase by 6-PTU follows first order kinetics, and is inhibited competitively by both arginine and (6R)-5,6,7,8-tetrahydro-L-biopterin, but is not accompanied by either a loss of heme-CO binding, heme fluorescence, or disassembly of dimeric structure. 2-Thiouracil behaves qualitatively identically to 6-PTU. Turnover-dependent inactivation of neuronal nitric oxide synthase by [2-14C]-2-thiouracil is accompanied by incorporation of radioactivity into the polypeptide chain. Ca2+-dependent NO formation by GH3 pituitary cells is inhibited by 6-PTU in a manner enhanced by depletion of either extracellular arginine or intracellular (6R)-5,6,7,8-tetrahydro-L-biopterin. These observations establish that 6-PTU is an alternate substrate, mechanism-based inactivator of the neuronal nitric oxide synthase isoform with the ability to suppress cellular NO formation.
authors.affiliation: Department of Pharmacology, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, 675 Hoes Lane, Piscataway, NJ 08854, USA. wolffdj@umdnj.edu
authors.forename: Donald J
authors.initials: DJ
authors.lastname: Wolff
authors.forename: Nathaniel
authors.initials: N
authors.lastname: Marks
mesh_terms: D000818:Animals; D013956:Antithyroid Agents / Q000494:pharmacology*; D001120:Arginine / Q000494:pharmacology; D001708:Biopterins / Q000031:analogs & derivatives* / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000494:pharmacology; D002248:Carbon Monoxide / Q000737:chemistry / Q000378:metabolism; D002250:Carbon Radioisotopes; D002956:Citrulline / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006418:Heme / Q000378:metabolism; D007700:Kinetics; D009569:Nitric Oxide / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D052248:Nitric Oxide Synthase Type I; D010911:Pituitary Neoplasms / Q000188:drug therapy / Q000378:metabolism; D011441:Propylthiouracil / Q000494:pharmacology*; D051381:Rats; D013889:Thiouracil / Q000493:pharmacokinetics / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D013956:Antithyroid Agents; D002147:Calmodulin; D002250:Carbon Radioisotopes; D004791:Enzyme Inhibitors; D001708:Biopterins; D002956:Citrulline; D009569:Nitric Oxide; D006418:Heme; D013889:Thiouracil; D011441:Propylthiouracil; D002248:Carbon Monoxide; D001120:Arginine; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; C496322:Nos1 protein, rat; C003402:sapropterin; D002118:Calcium