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Hydrogen‐tritium exchange of the random chain polypeptide
Author(s) -
Englander S. W.,
Poulsen A.
Publication year - 1969
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.1969.360070309
Subject(s) - chemistry , tritium , deprotonation , protonation , catalysis , hydrogen , amide , mole , alanine , activation energy , medicinal chemistry , stereochemistry , inorganic chemistry , amino acid , organic chemistry , biochemistry , ion , physics , nuclear physics
The Hydrogen–tritium exchange character of poly‐ D , L ‐alanine was studied in detail as a model for the hydrogen exchange behavior of the unhindered, polymeric peptide group. The random chain nature of poly‐ D , L ‐alanine was evident in the uniformity of exchange rate of all its hydrogens and in the similarity between this rate and that of random chain poly‐ D , L ‐lysine and other known, unhindered secondary amide groups. An equilibrium isotope effect favoring the binding of tritium over protium to the extent of 21% was measured. Specific acid and base catalysis of the exchange and the absence of detectable general catalysis were demonstrated. Apparent energy of activation is 17 kcal/mole for deprotonation, largely due to dependence of K w on temperature, and 15 kcal/mole for protonation, which correlates with the extreme apparent pK. The hydrogen –tritium exchange half‐time rate; of poly‐ D , L ‐alamine at any pH and temperature (T: °C) is given by the equation:\documentclass{article}\pagestyle{empty}\begin{document}$$ \[t_{\frac{1}{2}} \,(\min )\, = \,200\,\, \times \,10^{0.05{\rm T}} /\,[10^{{\rm pH} - 3} \, + \,10^{3 - {\rm pH}} ]\] $$\end{document}