Circular dichroic and fluoropolarimetric studies on tryptophyl residues in acid-induced isomerization of bovine plasma albumin.

The acid-induced isomerization (the N-F transition) and expansion of bovine plasma albumin were studied by measuring circular dichroic spectra and fluorescence polarization of tryptophyl residues. Decreases in the magnitude of ellipticities at 208, 222, 262 and 268 nm were observed in the N-F transition and acid-expansion. However, increases in the magnitude of ellipticities at 295-300 nm observed in the initial part of the N-F transition exactly correlated with the increase of rotational relaxation time of tryptophyl side chains obtained by fluorescence polarization measurement.