Changes in the secondary structure of protamine upon interaction with heparin. The complex formation was carried out at 20°C directly within the circular dichroism cuvette and was recorded using far UV circular dichroism spectra (185-260 nm) with a Chirascan circular dichroism spectrometer. The spectra of protamine and of protamine-heparin complexes were corrected for the baselines, path length, and concentration to obtain the wavelength-dependent mean residue δ ε values of the protamine-heparin complexes. Note that increasing heparin concentrations decreased the ellipticity values, indicating a decrease in the respective secondary structure content on a qualitative level.