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Helix‐coil stability constants for the naturally occurring amino acids in water. XXIII. Proline parameters from random poly(hydroxybutylglutamine‐ CO ‐ L ‐proline)
Author(s) -
Altmann K.H.,
Wójcik J.,
Vásquez M.,
Scheraga H. A.
Publication year - 1990
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360300112
Subject(s) - chemistry , copolymer , aminolysis , proline , glutamine , helix (gastropod) , amino acid , stereochemistry , polymer chemistry , polymer , organic chemistry , biochemistry , catalysis , ecology , snail , biology
Water‐soluble random copolymers containing L ‐proline and N 5 ‐(4‐hydroxybutyl)‐ L ‐glutamine were synthesized by copolymerization of the tripeptides H‐ L ‐Glu(OBzl)‐ L ‐Glu(OBzl)‐ L ‐Glu(OBzl)‐OH and H‐ L ‐Glu(OBzl)‐ L ‐Pro‐ L ‐Glu(OBzl)‐OH, using ben‐zotriazolyl‐N‐oxy‐tris(dimethylamino)‐phosphonium hexafluorophosphate as condensing reagent, and subsequent aminolysis of the Bzl ester groups with 4‐amino‐1‐butanol. These copolymers were found to contain significant amounts of N 5 ‐(4‐hydroxybutyl)‐ D ‐glutamine, thus requiring the synthesis of a binary copolymer containing only D ‐ and L ‐N 5 ‐(4‐hydroxybutyl)glutamine residues in order to evaluate the possible effects of the D ‐residues on the conformational properties of poly(hydroxybutylglutamine‐co‐ L ‐proline). The different copolymers were fractionated, and their thermally induced helix‐coil transition curves were obtained in water at neutral pH. When proper corrections were applied for the helix‐destabilizing properties of N 5 ‐(4‐hydroxybutyl)‐ D ‐glutamine, the Zimm‐Bragg parameters σ and s for L ‐proline could be deduced from the melting curves of poly (hydroxybutylglutamine‐co‐ L ‐proline). The results indicate that L ‐proline acts as a very strong helix breaker over the entire temperature range from 0 to 60°C.