Circular dichroic and perturbation spectra of aromatic chromophores in rabbit tropomyosin. Topography of tyrosine residues.

1. Difference spectra of tryosyl residues obtained on denaturation of tropomycosin with urea or guanidinium chloride indicate that strong hydrophobic environments exist in the native coiled-coil state. 2. Solvent perturbation difference spectra indicate that tyrosyl residues are partially accessible to the solvent. The accessiblity decreases with increasing size of the solvent molecules. 3. Spectral pH titration of tyrosyl residues cannot provide information on the tyrosyl accessibility because conformational change accompanies the increase in pH. 4. Circular dichroism of tyrosyl and phenylalanyl residues is consistent with the effect of imposed conformational rigidity on the partially asymmetrical vibrational fine structure of the 1Lb absorption band of phenyl and benzyl chromophores; the effect is reduced by 70% on unfolding of tropomyosin.