The optical properties of alpha 2-macroglobulin from normal and from cystic fibrosis plasma.

The alpha 2-macroglobulin (alpha 2-M) was purified from the plasma of normal individuals and from that of cystic fibrosis patients. The proteins exhibited identical optical properties. Both proteins have an absorbance coefficient of A = 1060 g . cm-2 at 280 nm. The circular dichroism spectra are identical and indicate about 45% beta-sheet structure and almost no alpha-helix. The spectra of solutions at pH 8.0 do not change when trypsin is added. The fluorescence spectra of the alpha 2-M measured at pH 8.0 have contributions by tyrosine and tryptophan residues. The fluorescence intensities are identical and are enhanced about 30% when trypsin is added in 2:1 molar ratios.