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Theory of melting of the triple helix poly (A + 2U) for a 1 : 2 mixture of Poly A to Poly U
Author(s) -
Goldstein Byron
Publication year - 1973
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.1973.360120302
Subject(s) - nucleation , helix (gastropod) , triple helix , chemistry , random coil , crystallography , thermodynamics , polymer chemistry , stereochemistry , physics , organic chemistry , circular dichroism , ecology , snail , biology
The Zimm‐Bragg theory is extended to treat the melting of the triple helix poly (A + 2U) for a solution with a 1 : 2 mole ratio of poly A to poly U. Only the case for long chains is considered. For a given set of parameters the theory predicts the fraction of segments in the triple helix, double helix, and random coil states as a function of temperature. Four nucleation parameters are introduced to describe the two order–disorder transitions (poly (A + 2U) ⇄ poly A + 2 poly U and poly (A + U) ⇄ poly A + poly U) and the single order–order transition (poly (A + 2U) ⇄ poly (A + U) + poly U). A relation between the nucleation parameters is obtained which reduces the number of independent parameters to three. A method for determining these parameters from experiment is presented. From the previously published data of Blake, Massoulié and Fresco 8 for [Na + ] = 0.04, we find σ T = 6.0 × 10 −4 , σ D = 1.0 × 10 −3 , and σσ* = 1.5 × 10 −3 . σ T and σ D are the nucleation parameters for nucleating a triple helix and double helix, respectively, from a random coil region. σσ* is the nucleation parameter for nucleating a triple helix from a double helix and a single strand. Melting curves are generated from the theory and compared with the experimental melting curves.