title: Symmetry distortion in the human hemoglobin tetramer induced by asymmetric ligation.
abstract: To investigate the conformational changes in human tetrameric (αβ)(2) hemoglobin upon binding of the first two ligands, we have measured the kinetics of reactions between 4,4'-dithiodipyridine and β93Cys sulfhydryl groups of four diliganded hemoglobins by using CO-bound Fe(II)-Ni(II) hybrids with and without β-β cross-linking. The data show that all the diliganded intermediates have high sulfhydryl reactivities, which are greater than or equal to that for the fully-liganded end state, especially when containing liganded α subunit(s). The results also reveal that both the asymmetrically (α1β1 and α1β2) diliganded species show similar high rates of sulfhydryl reactivity and biphasic kinetics, suggesting a new conformation but only slight functional distortion caused by asymmetric ligation.
authors.affiliation: Department of Physiology, Division of Biophysics, Jichi Medical University, 3311-1 Yakushiji, Shimotsuke, Tochigi 329-0498, Japan. shibayam@jichi.ac.jp
authors.forename: Naoya
authors.initials: N
authors.lastname: Shibayama
mesh_terms: D003432:Cross-Linking Reagents / Q000737:chemistry; D004220:Disulfides / Q000737:chemistry; D006454:Hemoglobins / Q000737:chemistry*; D006801:Humans; D007501:Iron / Q000737:chemistry; D009532:Nickel / Q000737:chemistry; D011487:Protein Conformation; D011725:Pyridines / Q000737:chemistry
chemical_list: D003432:Cross-Linking Reagents; D004220:Disulfides; D006454:Hemoglobins; D011725:Pyridines; C007542:4,4'-dipyridyl disulfide; D009532:Nickel; D007501:Iron