Helix-Coil Stability Constants for the Naturally Occurring Amino Acids in Water. 19. Isoleucine Parameters From Random Poly((Hydroxypropyl)Glutamine-co-L-Isoleucine)

• Published in: Macromolecules Vol. 14; no. 3; pp. 625 - 632
• Main Authors: Fredrickson, R A, Chang, M C, Powers, S P, Scheraga, HA
• Format: Journal Article
• Language: English
• Published: 01.01.1981
• Subjects: helix-coli transitions; poly((hydroxypropyl)glutamine-co-L-isoleucine); synthesis
• ISSN: 0024-9297

The synthesis and characterization of water-soluble random copolymers containing L-isoleucine and N super(5)-(3-hydroxypropyl)-L-glutamine, and the thermally induced helix-coil transitions of these copolymers in water, are described. The incorporation of L-isoleucine was found to increase the helix content of the polymers in water at all temperatures in the range of 0-70 degree C. The Zimm-Bragg parameters sigma and s for the helix-coil transition in poly(L-isoleucine) in water were deduced from an analysis of the copolymer melting curves in the manner described in earlier papers. The computed values of s indicate that L-isoleucine stabilizes helical sequences at all temperatures in the range of 0-60 degree C. The two nonpolar residues which are branched at their C super( beta ) atoms (L-isoleucine and L-valine) differ markedly in their helix-coil stability constants.