Conformational studies of hemoglobins using intrinsic fluorescence measurements

Front face fluorometry allows for the detection of intrinsic fluorescence in intact hemoglobins, and we have been able to assign the origin of this emission in Hb A to the tryptophan at beta 37 (Hirsch, R. E., Zukin, R. S., and Nagel, R. L. (1980) Biochem. Biophys. Res. Commun. 93, 432-439). We now report that this fluorescence in hemoglobin is sensitive to the R leads to T conformational transition. Comparison between liganded states of Hb A suggest a difference in the R structures of HbCO and HbO2. The T state induced by inositol hexaphosphate in the presence of methemoglobin A appears to be different from the T state of deoxyHb A. In agreement with chemical data our fluorescence studies of Hb H indicate that no R to T transition occurs in this hemoglobin, secondary to ligand binding. A slight conformational difference exists between deoxyHbH and COHbH. Hb Beth Israel, a low oxygen affinity mutant, shows unique fluorescence properties suggesting significant differences between the R and T forms relative to those of Hb A.