Contribution of ?140Tyr and ?37Trp to the near-UV CD spectra on quaternary structure transition of human hemoglobin A

Abstract

The CD band of human adult hemoglobin (Hb A) at 280 ∼ 290 nm shows a pronounced change from a small positive band to a definite negative band on the oxy (R) to deoxy (T) structural transition. This change has been suggested to be due to environmental alteration of Tyrs (α42, α140, and β145) or β37 Trp residues located at the α1β2 subunit interface by deoxygenation. In order to evaluate contributions of α140Tyr and β37Trp to this change of CD band, we compared the CD spectra of two mutant Hbs, Hb Rouen (α140Tyr→His) and Hb Hirose (β37Trp→Ser) with those of Hb A. Both mutant Hbs gave a distinct, but smaller negative CD band at 287nm in the deoxy form than that of deoxyHb A. Contributions of α140Tyr and β37Trp to the negative band at the 280 ∼ 290 nm region were estimated from difference spectra to be 30% and 26%, respectively. These results indicate that the other aromatic amino acid residues, α42Tyr and β145Tyr, at the α1β2 interface, are also responsible for the change of the CD band upon the R→T transition of Hb A. Chirality 12:216–220, 2000. © 2000 Wiley‐Liss, Inc.

Changes of near‐UV CD spectrum of human hemoglobin upon oxygen binding: A study of mutants at α42, α140, β145 tyrosine or β37 tryptophan

“…On the other hand, the contributions of the penultimate tyrosine residues (α140 and β145) to the CD change were estimated from the Δϵ values for Hb Rouen and rHb Thr‐β145 to be 32 and 27%, respectively. The value for Tyr‐α140 is fairly consistent with that of the previous study 5. According to Perutz et al,1 the penultimate tyrosine residues are firmly anchored in the pocket made by the F and H helices in the deoxy‐form.…”

“…Previously we estimated the contributions of Trp‐β37 and Tyr‐α140 to the negative CD band at 287nm in the deoxy‐form to be 26 and 30%, respectively, by comparing the CD spectra of Hb Hirose (Trp‐β37→Ser) and Hb Rouen (Tyr‐α140→His) with those of Hb A 5. However, we noticed that Hb Hirose had a high oxygen affinity and low cooperativity (Hill's n = 1.5) under the condition examined, indicating that it stayed on the R form even in the deoxy‐form and probably did not undergo the T→R transition.…”

Circular dichroism spectroscopy of tertiary and quaternary conformations of human hemoglobin entrapped in wet silica gels

“…The major effects are associated with the modification of the heme ligation state, which affects both the visible and the near‐UV regions (Ueda et al 1969). A residual contribution is attributed to a change in the optical activity of aromatic amino acids due to either tertiary or quaternary transitions (Perutz et al 1974b; Plese and Amma 1977; Li et al 2000a,b; Jin et al 2004). A comparison between the spectra of unliganded and liganded Hb in solution (Fig.…”

“…For example, the Zn heme of αZnβFe and αFeβZn hybrids does not bind oxygen, and consequently, the tetramer remains in a half‐saturated T state even in the presence of CO (Miyazaki et al 1999). From these studies, a spectral region around 260 nm was shown to depend almost exclusively on the electronic state of the heme (Zentz et al 1994), whereas the 280–290 nm region was shown to contain contributions from Tyrα42, Trpβ37, Tyrα140, and Tyrβ145 (Li et al 2000a, b; Jin et al 2004). These residues are located at the α 1 β 2 interface and, therefore, might be sensitive to the quaternary state of the tetramer (Perutz et al 1974b; Plese and Amma 1977).…”

Heme Orientation of Cavity Mutant Hemoglobins (His F8 → Gly) in Either α or β Subunits: Circular Dichroism, 1H NMR, and Resonance Raman Studies

“…We have studied the circular dichroism (CD) spectra of native human adult hemoglobin (Hb A) to elucidate the relationship between its structure and oxygen (O 2 ) binding function . O 2 binding sites of hemoglobin (Hb) and myoglobin (Mb) are heme (Fe‐protoporphyrin IX complex).…”