Changes of near-UV CD spectrum of human hemoglobin upon oxygen binding: A study of mutants at α42, α140, β145 tyrosine or β37 tryptophan
✍ Scribed by Yayoi Jin; Hiroshi Sakurai; Yukifumi Nagai; Masako Nagai
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 2004
- Tongue
- English
- Weight
- 75 KB
- Volume
- 74
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
Abstract
The deoxy‐form of human adult hemoglobin (Hb A) exhibits a distinct negative CD band at 287 nm that disappears in the oxy‐form. It has been suggested that the negative CD band is due to the environmental alteration of Tyr‐α42 or Trp‐β37 at the α~1~β~2~ contact upon deoxygenation. To evaluate the contributions of the aromatic residues at the α~1~β~2~ contact and the penultimate tyrosine residues of the α and β subunits (α140 and β145) to the negative CD band, three recombinant (r) Hbs (rHb Ser‐α42, rHb His‐β37, and rHb Thr‐β145) were produced in Escherichia coli, and we compared the near‐uv CD spectra of these three rHbs and Hb Rouen (Tyr‐α140→His) with the spectra of Hb A under the condition in which all mutant Hbs were able to undergo the T→R transition (Hill's n > 2.0). The contributions of Tyr‐α42, Trp‐β37, Tyr‐α140, and Tyr‐β145 to the negative CD band were estimated from changes in the ellipticity of the negative CD band at 287 nm to be 4, 18, 32, and 27%, respectively. These results indicate that environmental alteration of the penultimate tyrosine residues caused by the formation of salt bridges upon the R→T transition is primarily responsible for the negative CD band. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004