Salt-induced conformational change of random copolymers (Lys50Tyr50)n and (Lys50Phe50)n studied by 1H- and 13C-nuclear magnetic resonances. Aggregation behavior of helical segments |
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Authors: | Hazime Sait Toyokazu Ohki Masahiko Kodama Chikayoshi Nagata |
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Institution: | Hazime Saitô,Toyokazu Ohki,Masahiko Kodama,Chikayoshi Nagata |
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Abstract: | 1H- and 13C-nmr studies of conformational transitions of random amino acid copolymers containing aromatic residues (Lys50Tyr50)n and (Lys50Phe50)n in the presence of neutral salts were performed to serve as models of the aggregation behavior of polypeptides of biological significance. The 1H and 13C signal intensities of Tyr and Phe residues decreased preferentially with increasing concentration of neutral salts such as NaCl and NaClO4. This behavior contrasts with that of (Lys)n in the presence of similar neutral salts, where the displacement of the 13C signal is clearly seen on transition from the random-coil to the helical conformation. On the basis of the previous conformational studies, the loss of the peak areas is ascribed to the presence of immobilized helical segments by hydrophobic interaction between aromatic side chains. The remaining resonances are due to the residual random-coil regions, since the values of nuclear Overhauser enhancements and chemical shifts are unchanged in the presence and absence of the neutral salts. |
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