Dielectric and calorimetric studies of hydrated purple membrane

¹ Chalmers University of Technology
² Institut de Biologie Structurale

^* To whom correspondence should be addressed. E-mail: f5xjs{at}fy.chalmers.se.

Submitted on November 29, 2004
Revised on January 27, 2005
Accepted on 19 April 2005

	Abstract

Purple membranes (PM) from halobacteria were hydrated to 0.4 and 0.2 g H2O/g of PM and studied by dielectric spectroscopy and differential scanning calorimetry (DSC) between 120-300 K. The dielectric process, attributed to a local () relaxation of the confined supercooled water, shows an Arrhenius temperature behavior at low temperatures. In the case of the most hydrated PM a small deviation from the Arrhenius behavior occurs at 190-200 K together with a pronounced endothermic process and an increased activation energy. The observed cross-over is accompanied by a reduction of the interlayer spacing due to the partial loss of the inter-membrane water [M. Weik et.al submitted to Biophys. J]. All these effects at about 200 K are consistent with a scenario where the local relaxation process merges with a non-observable -relaxation of the interlayer water, giving rise to a more liquid-like behavior of the interfacial water. For the less hydrated sample the effects are less pronounced and shift to a slightly higher temperature.

Key Words: DSC, confine water, dielectric spectroscopy, dynamics, purple membrane, structural relaxation

This article has been cited by other articles:

				K. Wood, M. Plazanet, F. Gabel, B. Kessler, D. Oesterhelt, D. J. Tobias, G. Zaccai, and M. Weik Coupling of protein and hydration-water dynamics in biological membranes PNAS, November 13, 2007; 104(46): 18049 - 18054. [Abstract] [Full Text] [PDF]

				M. Weik, U. Lehnert, and G. Zaccai Liquid-Like Water Confined in Stacks of Biological Membranes at 200 K and Its Relation to Protein Dynamics Biophys. J., November 1, 2005; 89(5): 3639 - 3646. [Abstract] [Full Text] [PDF]