title: Role of hydrogen bonding to bound dioxygen in soybean leghemoglobin.
abstract: Electron spin echo envelope modulation (ESEEM) spectroscopy was applied to oxy cobaltous soybean leghemoglobin (oxyCoLb) in D2O at various pH values to investigate electron nuclear superhyperfine coupling to N epsilon of the proximal histidyl imidazole and to exchangeable deuterons. Two spectroscopically distinct forms of oxyCoLb, acid and neutral, were identified. In the acid form, a 0.82-MHz hyperfine coupling to 2H was found, indicating the presence of a hydrogen bond to bound O2. No hyperfine-coupled 2H was found in the neutral form. Nuclear hyperfine and nuclear quadrupole couplings to the proximal histidyl N epsilon in the acid form are smaller than those in the neutral form: Aiso = 2.22 MHz and e2qQ = 1.98 MHz for the acid form; Aiso = 2.90 MHz and e2qQ = 2.22 MHz for the neutral form. The differences are believed to result from the presence of a hydrogen bond to bound O2 in the acid form. A discussion of the contribution of this hydrogen bond to the pH-dependent O2 affinity of leghemoglobin is presented.
authors.affiliation: Department of Molecular Pharmacology, Albert Einstein College of Medicine, Yeshiva University, Bronx, New York 10461.
authors.forename: H C
authors.initials: HC
authors.lastname: Lee
authors.forename: J B
authors.initials: JB
authors.lastname: Wittenberg
authors.forename: J
authors.initials: J
authors.lastname: Peisach
mesh_terms: D003035:Cobalt; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D007501:Iron; D007874:Leghemoglobin / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism*; D011485:Protein Binding; D013025:Glycine max
chemical_list: D007874:Leghemoglobin; D003035:Cobalt; D007501:Iron; D010100:Oxygen