title: Effects of nitroglycerin/L-cysteine on soluble guanylate cyclase: evidence for an activation/inactivation equilibrium controlled by nitric oxide binding and haem oxidation.
abstract: GTN (nitroglycerin; glycerol trinitrate) causes dilation of blood vessels via activation of nitric oxide (NO)-sensitive sGC (soluble guanylate cyclase), a heterodimeric haem protein that catalyses the conversion of GTP into cGMP. Activation of sGC by GTN requires enzymatic or non-enzymatic bioactivation of the nitrate. Based on insufficient NO release and lack of spectroscopic evidence for formation of NO-sGC, the cysteine (Cys)-dependent activation of sGC by GTN was proposed to occur in an NO-independent manner. This extraordinary claim is questioned by the present findings. First, the effect of GTN/Cys was blocked by the NO scavenger oxyhaemoglobin, the superoxide-generating compound flavin mononucleotide and the haem-site sGC inhibitor ODQ (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one). Secondly, at equi-effective concentrations, GTN/Cys and the NO donor 2,2-diethyl-1-nitroso-oxyhydrazine released identical amounts of NO. Finally, at sufficiently high rates of NO release, activation of sGC by GTN/Cys was accompanied by a shift of the Soret band from 431 to 399 nm, indicating formation of NO-sGC. In the absence of Cys, GTN caused haem oxidation, apparent as a shift of the Soret band to 392 nm, which was accompanied by inactivation of the NO-stimulated enzyme. These results suggest that the effect of GTN/Cys is the result of an activation/inactivation equilibrium that is controlled by the rate of NO release and haem oxidation.
authors.affiliation: Department of Pharmacology and Toxicology, Karl-Franzens-Universität Graz, A-8010 Graz, Austria.
authors.forename: Antonius C F
authors.initials: AC
authors.lastname: Gorren
authors.forename: Michael
authors.initials: M
authors.lastname: Russwurm
authors.forename: Alexander
authors.initials: A
authors.lastname: Kollau
authors.forename: Doris
authors.initials: D
authors.lastname: Koesling
authors.forename: Kurt
authors.initials: K
authors.lastname: Schmidt
authors.forename: Bernd
authors.initials: B
authors.lastname: Mayer
mesh_terms: D000818:Animals; D002417:Cattle; D003545:Cysteine / Q000378:metabolism / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D006162:Guanylate Cyclase; D006418:Heme / Q000378:metabolism*; D006834:Hydrazines / Q000494:pharmacology; D008027:Light; D008168:Lung / Q000201:enzymology; D009569:Nitric Oxide / Q000378:metabolism*; D009589:Nitrogen Oxides / Q000494:pharmacology; D005996:Nitroglycerin / Q000378:metabolism / Q000494:pharmacology*; D010084:Oxidation-Reduction / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D000071756:Soluble Guanylyl Cyclase
chemical_list: D006834:Hydrazines; D009589:Nitrogen Oxides; D018160:Receptors, Cytoplasmic and Nuclear; D009569:Nitric Oxide; D006418:Heme; C084012:1,1-diethyl-2-hydroxy-2-nitrosohydrazine; D006162:Guanylate Cyclase; D000071756:Soluble Guanylyl Cyclase; D005996:Nitroglycerin; D003545:Cysteine