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Isodichroic point and the β–random coil transition of poly( S ‐carboxymethyl‐ L ‐cysteine) and poly( S ‐carboxyethyl‐ L ‐cysteine) in the absence of added salt
Author(s) -
Maeda Hiroshi,
Ooi Kenta
Publication year - 1981
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.1981.360200712
Subject(s) - chemistry , random coil , potentiometric titration , cysteine , titration , salt (chemistry) , stacking , polymer chemistry , crystallography , intrinsic viscosity , stereochemistry , polymer , circular dichroism , organic chemistry , ion , enzyme
The β‐coil transition of poly( S ‐carboxymethyl‐ L ‐cysteine) (poly[Cys(CH 2 CO 2 H)]) and poly( S ‐carboxyethyl‐ L ‐cysteine) (poly[Cys((CH 2 ) 2 CO 2 H)]) was followed by CD, potentiometric titration, and viscosity in the absence of added salt. These different properties give consistent results for poly[Cys((CH 2 ) 2 CO 2 H)]. The CD spectra of poly[Cys(CH 2 CO 2 H)] change considerably with the degree of neutralization α even for a low‐molecular‐weight sample incapable of forming the β‐structure. Because of the superposition of this additional effect, the dependence of CD on α is inconsistent with titration data for the case of poly[Cys(CH 2 CO 2 H)], particularly when the n π transition is used to follow the β‐coil transition. The change of CD inherent to the β‐coil transition is characterized by an isodichroic point: 215 nm for poly[Cys((CH 2 ) 2 CO 2 H)] and 218 nm for poly[Cys(CH 2 CO 2 H)]. A criterion supporting the stacking of the pleated sheet is suggested based on the isodichroic point.