Amide I' decomposition of salmine and squid protamine in purified sperm nuclei. The DNA contribution was subtracted as described in Methods. Spectra were measured in D2O. The buffer was 10 mM HEPES plus 140 mM NaCl, pH 7.0 at 20°C. The concentration of nuclei expressed as DNA concentration was 5 mg/ml. The peak at 1609 cm-1 corresponds to the arginine side chain plus, in the case of squid protamine (lower panel), a contribution from tyrosine side chains. The α-helix component is highlighted in red and the random coil/flexible regions are highlighted in orange.
Roque et al. BMC Structural Biology 2011 11:14 doi:10.1186/1472-6807-11-14