Helix-coil stability constants for the naturally occurring amino acids in water. IX. Glutamic acid parameters from random poly(hydroxybutylglutamine-co-L-glutamic acid)
The synthesis and characterization of water-soluble random copolymers containing L-glutamic acid with N5-(4-hydroxybutyl)-L-glutamine and the thermally induced helix-coil transitions of these copolymers in water and in 0.1 N KCl are described. The incorporation of L-glutamic acid was found to increase the helix content of the polymer at low pH and to decrease it at high pH even though the presence of 0.1 N KCl effectively eliminated the difference between the electrostatic free energies of the helix and the coil. The Zimm-Bragg parameters sigma and s for the helix-coil transition in poly(L-glutamic acid) in water and in 0.1 N KCl were deduced from an analysis of the melting curves of the copolymers in the manner described in earlier papers. The synthesis of N-acetyl-N'-methylglutamic acid amide and its titration, as well as that of the copolymers and poly(L-glutamic acid), in 0.1 N KCl are described.