Changes of Near-UV Circular Dichroism Spectra of Human Hemoglobin upon the R->T Quaternary Structure Transition

摘要

Human adult hemoglobin (Hb A) exhibits a distinct negative CD band at 287 nm in the deoxy-form (T, tense), but this band disappears in the oxy-form (R, relaxed) It was suggested that the environmental alteration of aromatic amino acids, Tyr-a42 and/or Trp-p.37, at the a^2 subunit contact contributed to the negative CD band in the deoxy-form, However, precise assignment of aromatic amino acids responsible for the negative CD band still remains unsettled, To evaluate contribution of the aromatic amino acid residues to the negative CD band upon the R -?T structure transition, we examined near-UV CD spectra of four mutant hemoglobins, two at the cciP2 subunit contact, recombinant hemoglobin (rHb) (Tyr-a42->Ser) and rHb (Trp-P37->His), and the other two at the penultimate Tyr, rHb (Tyr-pi45->Thr) and Hb Rouen (Tyr-cd40->His).