Helix-Coil Stability Constants for the Naturally Occurring Amino Acids in Water. 17. Threonine Parameters from Random Poly(hydroxybutylglutamine-co-L-threonine)

The synthesis and characterization of water-soluble random copolymers containing L-threonine with N5-(4-hydroxybutyl)-L-glutamine and the thermally induced helix-coil transitions of these copolymers in water are described. The incorporation of L-threonine was found to decrease the helix content of the copolymers in water at all temperatures. The Zimm-Bragg parameters σ and s for the helix-coil transition of poly(L-threonine) in water were deduced from an analysis of the melting curves of the copolymers in the manner described in earlier papers. The computed values of s indicate that L-threonine destabilizes helical sequences at all temperatures in the range of 0-70.