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Circular dichroism and the pH‐induced β‐coil transition of poly(S‐carboxymethyl‐ L ‐cysteine) and its side‐chain homolog
Author(s) -
Ikeda Shoichi,
Fukutome Akira,
Imae Toyoko,
Yoshida Tomohiko
Publication year - 1979
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.1979.360180210
Subject(s) - chemistry , circular dichroism , cysteine , aqueous solution , side chain , residue (chemistry) , crystallography , hydrogen bond , cotton effect , salt (chemistry) , stereochemistry , polymer chemistry , polymer , molecule , organic chemistry , enzyme
The CD of aqueous solutions of poly(S‐carboxymethyl‐ L ‐cysteine) and poly(S‐carboxyethyl‐ L ‐cysteine) has been measured at different pH, and the pH‐induced β‐coil transition is observed by changes in residue ellipticity of dichroic bands around 200 and 225 nm. The residue ellipticity at 200 nm of the former polypeptide is twice as large as that of the latter, when the β‐conformation is formed in solution. However, the β‐conformation of the latter polypeptide is more stable against electrostatic repulsion than that of the former. The transition curve of poly(S‐carboxymethyl‐ L ‐cysteine) has also been determined for different molecular weights. The curves were found to be completely coincident with one another if the degree of polymerization were higher than about 100. Such a transition curve is generally divided into three steps: initiation, cooperative formation, and rearrangement of hydrogen bonds. The cooperative step is very sharp, occurring at a constant pH. These steps become agglomerated into two or one when the polypeptide concentration or added salt concentration is increased.