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Helix–coil dynamics of a Z‐helix hairpin
Author(s) -
Antosiewicz J.,
German M. W.,
Van De Sande J. H.,
Porschke D.
Publication year - 1988
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.360270810
Subject(s) - chemistry , helix (gastropod) , enthalpy , crystallography , thermodynamics , atmospheric temperature range , temperature jump , nucleation , physics , organic chemistry , ecology , snail , biology
The helix–coil transition of a Z‐helix hairpin formed from d(C‐G) 5 T 4 (C‐G) 5 has been characterized by equilibrium melting and temperature jump experiments in 5 M NaClO 4 and 10 m M Na 2 HPO 4 , pH 7.0. The melting curve can be represented by a simple all‐or‐none transition with a midpoint at 81.6 ± 0.4°C and an enthalpy change of 287 ± 15 kJ/mole. The temperature jump relaxation can be described by single exponentials at a reasonable accuracy. Amplitudes measured as a function of temperature provide equilibrium parameters consistent with those derived from equilibrium melting curves. The rate constants of Z‐helix formation are found in the range from 1800 s −1 at 70°C to 800 s −1 at 90°C and are associated with an activation enthalpy of −(50 ± 10) kJ/mole, whereas the rate constants of helix dissociation are found in the range from 200 s −1 at 70°C to 4500 s −1 at 90°C with an activation enthalpy +235 kJ/mole. These parameters are consistent with a requirement of 3–4 base pairs for helix nucleation. Apparently nucleation occurs in the Z‐helix conformation, because a separate slow step corresponding to a B to Z transition has not been observed. In summary, the dynamics of the Z‐helix–coil transition is very similar to that of previously investigated right‐handed double helices.