Dielectric and Calorimetric Studies of Hydrated Purple Membrane

• Published in: Biophysical journal Vol. 89; no. 5; pp. 3120 - 3128
• Main Authors: Berntsen, Peter, Bergman, Rikard, Jansson, Helén, Weik, Martin, Swenson, Jan
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.11.2005; Biophysical Society
• Subjects: Biophysics; Calorimetry - methods; Calorimetry, Differential Scanning; Dielectrics; Differential scanning calorimetry; Electrophysiology; Euryarchaeota - metabolism; Kinetics; Lipids - chemistry; Membranes; Models, Statistical; Purple Membrane - metabolism; Spectrum Analysis; Temperature; Water - chemistry
• ISSN: 0006-3495; 1542-0086; 1542-0086
• DOI: 10.1529/biophysj.104.057208

Purple membranes (PM) from halobacteria were hydrated to ∼0.4 and ∼0.2g H2O/g of PM and studied by dielectric spectroscopy and differential scanning calorimetry between 120 and 300K. The dielectric process, attributed to a local (β) 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 190–200K together with a pronounced endothermic process and an increased activation energy. The observed crossover is accompanied by a reduction of the interlayer spacing due to the partial loss of the intermembrane water. All these effects at ∼200K are consistent with a scenario where the local relaxation process merges with a nonobservable α-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.