title: The contact sites of sickle hemoglobin as seen by spin probe-spin label techniques.
abstract: The spin-labeled tryptophan (TrpSL) was used as a structural probe of hemoglobin (Hb) contact sites. The electron paramagnetic resonance spectral data indicated that the probe exhibits weak binding to Hb with a dissociation constant of 3.2 x 10(-5) and 4.0 mol bound per Hb tetramer. The spectrum suggested that the bound tryptophan was 'partially immobilized' with a correlation time reflecting the environment of the tryptophan binding site of 8.5 s. The topology of the contact sites was investigated by using a dual spin label methodology in which TrpSL and 2H-15N covalently bound to B 93 cysteine residue were used. The electron spin resonance spectral data suggested that the tryptophan binding sites were located within 8-10 A of the nitroxide free radical of spin-labeled Hb. The environment of the contact sites is discussed.
authors.affiliation: Atlanta University, Chemistry Department, Ga.
authors.forename: H M
authors.initials: HM
authors.lastname: Zeidan
mesh_terms: D000755:Anemia, Sickle Cell / Q000097:blood; D001665:Binding Sites; D003497:Cyclic N-Oxides; D003545:Cysteine / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D006451:Hemoglobin, Sickle / Q000378:metabolism*; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D013113:Spin Labels; D014364:Tryptophan / Q000378:metabolism*
chemical_list: D003497:Cyclic N-Oxides; D006451:Hemoglobin, Sickle; D006454:Hemoglobins; D013113:Spin Labels; C017480:4-maleimido-2,2,6,6-tetramethylpiperidinooxyl; D014364:Tryptophan; D003545:Cysteine