Reversal of the Mg sup (++) -induced B-to-Z transition of poly[d (G-C)] with hydrostatic pressure.

The rate and extent of the conformational transition of poly[d (G-C)] from a right-handed B helix to a left-handed Z helix is sensitive to moderate amounts of hydrostatic pressure. The application of 220 MPa of pressure at 22C during the Mg sup (++) -induced B-to-Z transition causes the reaction to reverse towards the formation of the B form. The rate of this back-reaction is dependent upon the concentration of Mb sup (++). This is in contrast with the behavior of the transition initiated by 3.5 M NaCl which is slowed but not reversed at this pressure. These results emphasize the role of ion hydration in the B-to-Z transition.