The effect of ergosterol on dipalmitoylphosphatidylcholine bilayers: a deuterium NMR and calorimetric study

¹ National Central University, Taiwan
² University of Western Ontario, Canada
³ Roskilde University Center, Denmark
⁴ Simon Fraser University, Canada

^* To whom correspondence should be addressed. E-mail: jthewalt{at}sfu.ca.

Submitted on August 17, 2004
Revised on September 25, 2004
Accepted on 19 November 2004

	Abstract

We have studied the effect of ergosterol (erg), an important component of fungal plasma membranes, on the physical properties of dipalmitoylphosphatidylcholine (DPPC) multibilayers using deuterium nuclear magnetic resonance (²H NMR) and differential scanning calorimetry (DSC). For the ²H NMR experiments the sn-1 chain of DPPC was perdeuterated and NMR spectra were taken as a function of temperature and erg concentration. The phase diagram, constructed from the NMR spectra and the DSC thermograms, exhibits both solid ordered(so)+liquid ordered (lo) and liquid disordered (ld)+lo phase coexistence regions with a clear three-phase line. This is the first demonstration that lo domains exist in liquid crystalline membranes containing erg. The domain sizes in the ld+lo phase coexistence region were estimated by analyzing the exchange of labeled DPPC between the two regions, and depend on erg concentration. The DPPC-erg phase diagram is similar to that of several PC-cholesterol multibilayer systems (Vist and Davis, 1990, Biochemistry 29:451-464; Thewalt and Bloom, 1992, Biophys. J. 63:1176-1181) except that the so+lo and ld+lo phase coexistence regions are considerably broader.

Key Words: H NMR, DSC, ergosterol, phase diagram, phospholipid

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