The detection of hemoglobin dimers by intrinsic fluorescence

We have found that the intrinsic fluorescence emission maxima of oxy, met, and cyanmet hemoglobins have a concentration dependent shift to longer wavelengths. For oxy-hemoglobin, this effect is increased in the presence of 3M NaCl. At the protein concentrations studied, these liganded hemoglobins undergo dimerization. In contrast, horse-heart met myoglobin (which is a monomer), and deoxy Hb A and Hb Beth Israel (that have greatly decreased dissociation constants), exhibited a significantly smaller shift in fluorescence maxima. We conclude that hemoglobin dimers exhibit a bathochromic shift with respect to the tetramer. This shift is probably due to the increase in surface exposure of beta 37 Trp that occurs during hemoglobin dimerization.