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Tritium–hydrogen exchange of poly‐ L ‐glutamic acid in aqueous solutions
Author(s) -
Ikegami Akira,
Yamamoto Sadaaki,
Oosawa Fumio
Publication year - 1965
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.1965.360030506
Subject(s) - chemistry , random coil , tritium , aqueous solution , polymer , molecule , dispersion (optics) , proton , hydrogen , glutamic acid , kinetics , optical rotatory dispersion , analytical chemistry (journal) , crystallography , chromatography , amino acid , organic chemistry , circular dichroism , nuclear physics , biochemistry , physics , quantum mechanics , optics
Abstract To investigate the flexibility or motility of the secondary structure of poly‐ L ‐glutamic acid, a simple model molecule of proteins, the kinetics of the tritium–hydrogen exchange of this polymer in aqueous solutions was followed at various pH values by use of a freeze‐drying technique and a liquid scintillation counter. The most essential point of the experimental results is that all of the protons (or isotopes) attached to peptide nitrogens were exchanged according to a simple first‐order reaction and the rate was proportional to the fraction of random coil conformation determined by optical rotatory dispersion measurements. This means that the tritium attached to a peptide unit is exchangeable with a proton in water only when this unit is contained in the random coil structure and that the interchange of each unit between helical and random coil conformations takes place as a result of thermal fluctuation at very high frequency, although the average helical content of each molecule has a definite value.