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Journal Article

Helix-coil dynamics of a Z-helix hairpin.

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Antosiewicz,  J.
Abteilung Biochemische Kinetik, MPI for biophysical chemistry, Max Planck Society;

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Porschke,  D.
Abteilung Biochemische Kinetik, MPI for biophysical chemistry, Max Planck Society;

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Citation

Antosiewicz, J., German, M. W., Van De Sande, J. H., & Porschke, D. (1988). Helix-coil dynamics of a Z-helix hairpin. Biopolymers, 27(8), 1319-1327. doi:10.1002/bip.360270810.


Cite as: http://hdl.handle.net/11858/00-001M-0000-002D-4CE9-A
Abstract
The helix–coil transition of a Z-helix hairpin formed from d(C-G)5T4(C-G)5 has been characterized by equilibrium melting and temperature jump experiments in 5M NaClO4 and 10 mM Na2HPO4, 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.