A fluorescent dye 1-anilino-8-naphthalene sulfonate was complexed with human apohemoglobin and sperm whale apomyoglobin. Nanosecond fluorescencepolarization kinetics were measured for each of these complexes in KCl solutions to obtain their fluorescence lifetimes and rotational correlation times. The rotational correlation time of apohemoglobin-dye complex was found to be 21 ns, which was about twice that of apomyoglobin-dye complex, 11 ns. These values were constant over an ionic strength range from 0 to 1.7. Circular dichroism spectra (215-300 nm) and fluorescence lifetimes of the complexes were also found to be independent of the ionic strength, indicating that no gross conformational change occurs with the change in the salt concentration. These results suggest that apohemoglobin remains dimeric over the ionic-strength range examined.
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