Contribution of alpha 140Tyr and B37Trp to the near-UV CD spectra on quaternary structure transition of human hemoglobin A

The CD band of human adult hemoglobin (Hb A) at 280 similar to 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 su ggested to be due to environmental alteration of Tyrs (alpha 42, alpha 140, and beta 145) or beta 37 Trp residues located at the alpha 1 beta 2 subuni t interface by deoxygenation. In order to evaluate contributions of alpha 1 40Tyr and beta 37Trp to this change of CD band, we compared the CD spect ra of two mutant Hbs, Hb Rouen (alpha 140Tyr-->His) and Hb Hirose (beta 37Trp -->Ser) with those of Hb A. Both mutant Hbs gave a distinct, but smaller ne gative CD band at 287nm in the deoxy form than that of deoxyHb A. Contribut ions of alpha 140Tyr and beta 37Trp to the negative band at the 280 similar to 290 nm region were estimated from difference spectra to be 30% and 26%, respectively. These results indicate that the other aromatic amino acid re sidues, alpha 42Tyr and beta 145Tyr, at the alpha 1 beta 2 interface, are a lso responsible for the change of the CD band upon the R-->T transition of Hb A. (C) 2000 Wiley-Liss, Inc.