Nanosecond dynamics of tryptophans in different conformational states of apomyoglobin proteins

Fluorescence anisotropy kinetics were employed to quantify the nanosecond m obility of tryptophan residues in different conformational states (native, molten globule, unfolded) of apomyoglobins. Of particular interest is the s imilarity between the fluorescence anisotropy decays of tryptophans in the native and molten globule states. We find that, in these compact states, tr yptophan residues rotate rapidly within a cone of semiangle 22-25 degrees a nd a correlation time of 0.5 ns, in addition to rotating together with the whole protein with a correlation time of 7-11 ns. The similar nanosecond dy namics of tryptophan residues in both states suggests that the conformation changes that distinguish the molten globule and native states of apomyoglo bins originate from either subtle, slow rearrangements or fast changes dist ant from these tryptophans.