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Biophys J, June 2001, p. 2536-2545, Vol. 80, No. 6
and
*Department of Biochemistry, George S. Wise Faculty of Life
Sciences, Tel Aviv University, Ramat Aviv 69978 Israel, and
D-Pharm Ltd., Kiryat Weizmann Science Park, Rehovot
76123, Israel
Valproic acid (VPA) is a short, branched fatty acid with
broad-spectrum anticonvulsant activity. It has been suggested that VPA
acts directly on the plasma membrane. We calculated the free energy of
interaction of VPA with a model lipid bilayer using simulated annealing
and the continuum solvent model. Our calculations indicate that VPA is
likely to partition into the bilayer both in its neutral and charged
forms, as expected from such an amphipathic molecule. The calculations
also show that VPA may migrate (flip-flop) across the membrane;
according to our (theoretical) study, the most likely flip-flop path at
neutral pH involves protonation of VPA pending its insertion into the
lipid bilayer and deprotonation upon departure from the other side of
the bilayer. Recently, the flip-flop of long fatty acids across lipid
bilayers was studied using fluorescence and NMR spectroscopies.
However, the measured value of the flip-flop rate appears to depend on
the method used in these studies. Our calculated value of the flip-flop
rate constant, 20/s, agrees with some of these studies. The limitations
of the model and the implications of the study for VPA and other fatty acids are discussed.
Biophys J, June 2001, p. 2536-2545, Vol. 80, No. 6
© 2001 by the Biophysical Society 0006-3495/01/06/2536/10 $2.00
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