Structural Calorimetry of Main Transition of Supported DMPC Bilayers by Temperature-Controlled AFM

• Published in: Biophysical journal 2004-10, Vol.87 (4), p.2522-2531
• Main Authors: Enders, O., Ngezahayo, A., Wiechmann, M., Leisten, F., Kolb, H.-A.
• Format: Article
• Language: English
• Subjects: Calcium - chemistry; Calorimetry - methods; Dimyristoylphosphatidylcholine - chemistry; Heat; Heptanol - chemistry; Image Interpretation, Computer-Assisted - methods; Lipid Bilayers - chemistry; Lipids; Membrane Fluidity; Membranes; Membranes, Artificial; Microscopy, Atomic Force - methods; Molecular Conformation; Molecules; Phase Transition; Surface Properties; Temperature; Thermodynamics; Transition Temperature
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1529/biophysj.104.040105

Atomic force microscopy at high temperature resolution ( Δ T ≲ 0.1   K ) provided a quantitative structural calorimetry of the transition from the fluid ( L α )- to the gel ( P β ′ )-phase of supported dimyristoylphosphatidylcholine bilayers. Besides a determination of the main transition temperature ( T 0) and the van’t Hoff transition enthalpy (Δ H vH), the structural analysis in the nm-scale at T close to T 0 of the ripple phase allowed an experimental estimation of the area of cooperative units from small lipid domains. Thereby, the corresponding transition enthalpy (Δ H) of single molecules could be determined. The lipid organization and the corresponding parameters T 0 and Δ H vH (Δ H) were modulated by heptanol or external Ca 2+ and compared with physiological findings. The size of the cooperative unit was not significantly affected by the presence of 1 mM heptanol. The observed linear relationship of Δ H vH and T 0 was discussed in terms of a change in heat capacity.