J. Chim. Phys.
Volume 65, 1968
|Page(s)||53 - 53|
|Published online||28 May 2017|
Dynamics of conformation changes in helical macromolecules
Max-Planck-Institut für physikalische Chemie, Göllingen, Germany.
The kinetics of conformation changes helix-random coil habe been studied for different macromolecular systems. For high molecular weight systems the mechanisms are based on an interplay between nucleation and propagation of structure. Characteristic times have been found for the different types of helical molecules, i. e. single-, double- and triple-stranded helices of polypeptides and polynucleotides in solution. These times can be correlated with the time constants of elementary steps. The formation and disruption of a single hydrogen bond requires only a very short time of the order of magnitude of 10–10 sec. The helix coil transformation of α-helices thus can occur within fractions of microseconds. On the other hand conformation changes of the helical structures of polyproline require time constants of the order of magnitude of hours (with quite high activation energies) since rotation around a CN-bond in the polypeptide backbone is slow (time range around a second).
The melting of double stranded helices of polynucleotides requires disruption of base pairs - held together by H-bonds and stabilized by stacking interactions - as well as unwinding of the strands. The correlation between the elementary steps of base pairing and the cooperative helix formation has been studied in more detail with oligonucleotides of the chain length 3 to 10. The time constants of the elementary steps of base pairing are found around 10–7 sec whereas the total cooperative process of helix coil transformation requires half times in the millisecond region. For high molecular weight DNA the unwinding process is found to be quite slow, half times are of the order of magnitude of seconds to minutes, a time range which has been found also for triple stranded helices of lower molecular weights.
Studies of this kind yield a detailed picture of the nature of information transfer by cooperative complementary interactions.
© Paris : Société de Chimie Physique, 1968