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Conformation of poly( L ‐arginine). II. Complexes with polyanions
Author(s) -
Mita Kazuei,
Ichimura Sachiko,
Zama Mitsuo
Publication year - 1978
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.1978.360171204
Subject(s) - chemistry , polyelectrolyte , polynucleotide , glutamic acid , arginine , helix (gastropod) , aspartic acid , steric effects , crystallography , stereochemistry , urea , amino acid , polymer chemistry , biochemistry , organic chemistry , polymer , ecology , snail , biology
Abstract Conformaitons of poly( L ‐arginine)/polyanion complexes were studies by CD measurements. The polyanions were the homoplolypeptides poly( L ‐glutamic acid) and poly( L ‐aspartic acid); the synthetic polyelectrolytes and polyethylenesulfonate; and the polynucleotides were native DNA, denatured DNA, and poly(U). It was found that poly( L ‐arginine) forms the α‐helical conformation by interacting with the acidic homopolypeptides and the synthetic anionic polyelectrolytes. In each complex, poly( L ‐glutamic acid) is in the α‐helical conformation, whereas poly( L ‐aspartic acid) is mostly in the random structure. The poly( L ‐glutamic acid) complex changed into the β‐sheet structure at the transition temperature about 65°C in 0.01 M cacodylate buffer (pH 7). Even in the presence of 5 M urea, this complex remained in the α‐helical conformation at room temperature. The existence of the stable complex of α‐helical poly( L ‐arginine) and α‐helical poly( L ‐glutamic acid) was successfully supported by the model building study of the complex. The α‐helix of poly( L ‐arginine) induced by binding with polyacrylate was the most stable of the poly( L ‐arginine)‐polyanion complexes examined as evidenced by thermal and urea effects. The lower helical content of the polyethylenesulfonate‐complexed poly( L ‐aginine) was explained in terms of the higher charge density of the polyanion. On the other hand, native DNA, denatured DNA, and poly(U) were not effective in stabilizing the helical structure of poly( L ‐arginine). This may be due to the rigidity of polyanions and to the steric hindrance of bases. Furthermore, the distinitive structual behavior of poly( L ‐arginine) and poly( L ‐lysine) regarding polyanion interaction has been noticed throughout the study.