A fluorescence decay time study of tryptophan in isolated hemoglobin subunits

The time-resolved fluorescence behavior of tryptophan residues in isolated human hemoglobin subunits was determined using a sync-pumped dye laser system and time-correlated single photon counting detection. Two decay components having values near 80 ps and 2 ns were found in the fluorescence decay of the alpha-subunit. The data for the beta-chains were best fitted with 3 decay components of 90 ps, 2.5 ns and 6.4 ns. We propose that the decay times correspond to conformations of the proteins in which the disposition of the tryptophan to the heme residue differs.