Helix--coil stability constants for the naturally occurring amino acids in water. X. Tyrosine parameters from random poly(hydroxypropylglutamine-co-L-tyrosine).

The synthesis and characterization of water-soluble random copolymers containing L-tyrosine with N2-(3-hydroxypropyl)-L-glutamine are described, and the thermally induced helix--coil transitions of these copolymers in water have been studied. The incorporation of L-tyrosine was found to increase the helix content of the polymers at all temperatures. The Zimm-Bragg parameters sigma and sigma for the helix--coil transition in poly(L-tyrosine) in water were deduced from an analysis of the melting curves of the copolymers in the manner described in earlier papers. The large value of sigma indicates that, in water, tyrosine has a tendency to promote helix--coil boundaries at all temperatures; the values of sigma indicate that this residue enhances helix growth at low temperature and reduces it at high temperature.