title: Effect of strain in the proximal ligand on the binding of nitric oxide and carbon monoxide to chelated protoheme complexes.
abstract: The binding of NO and CO to chelated protoheme-l-histidine methyl ester (HM-H), protoheme-glycyl-l-histidine methyl ester (HM-GH), and free protoheme (HM) has been studied in methanol-DMSO solution. In all cases, the NO adducts are five-coordinated, indicating that binding of NO occurs with displacement of the axial base, and confirms the strong negative trans effect exerted by NO in heme complexes, though it is found that the presence of strain in the iron-histidine bond of HM-H has a positive influence on NO binding, making it thermodynamically more favorable than for HM-GH. The equilibrium constants thus decrease in the series: HM > HM-H > HM-GH. In contrast to NO, CO has a positive trans effect, and therefore, an opposite trend is observed in the binding of this ligand to the heme complexes.
authors.affiliation: Dipartimento di Chimica Inorganica, Metallorganica e Analitica, Università di Milano, Istituto ISTM-CNR, Via Venezian 21, 20133 Milano, Italy.
authors.forename: Michele
authors.initials: M
authors.lastname: Gullotti
authors.forename: Laura
authors.initials: L
authors.lastname: Santagostini
authors.forename: Enrico
authors.initials: E
authors.lastname: Monzani
authors.forename: Luigi
authors.initials: L
authors.lastname: Casella
mesh_terms: D002248:Carbon Monoxide / Q000737:chemistry*; D004121:Dimethyl Sulfoxide / Q000737:chemistry*; D004305:Dose-Response Relationship, Drug; D006418:Heme / Q000737:chemistry*; D006639:Histidine / Q000737:chemistry; D007093:Imidazoles / Q000737:chemistry; D007501:Iron / Q000737:chemistry; D008024:Ligands; D000432:Methanol / Q000737:chemistry; D008956:Models, Chemical; D015394:Molecular Structure; D009569:Nitric Oxide / Q000737:chemistry*; D013314:Stress, Mechanical; D013816:Thermodynamics
chemical_list: D007093:Imidazoles; D008024:Ligands; D009569:Nitric Oxide; D006418:Heme; D006639:Histidine; D002248:Carbon Monoxide; D007501:Iron; D000432:Methanol; D004121:Dimethyl Sulfoxide