Sugars favour formation of hexagonal (H II) phase at the expense of lamellar liquid-crystalline phase in hydrated phosphatidylethanolamines

Abstract

The disaccharides, sucrose and trehalose, markedly decreased (up to 17-13C°) the temperature of the lamellar to hexagonal (L α →H II) phase transition and simultaneously increase by 2–4 C° the temperature of the lamellar gel to lamellar liquid-crystal (L β →L α) phase transition in hydrated dihexadecylphosphatidylethanolamine and distearoylphosphatidylethanolamine. These two transitions merge and convert into a single L β-H II phase transition when dispersed in 2.4 M sucrose. These results are inconsistent with recent reports by Crowe et al. (1987) Biochem. J. 242, 1–10; (1988) Biochim. Biophys. Acta 947, 367–394) which suggest that trehalose stabilizes the L α phase relative to the H II phase and shifts upwards beyond detectability the L α-H II transition. The present results are considered as a manifestation of the Hofmeister effect in which the sugars act as kosmotropic reagents stabilizing the structure of bulk water. This tends to decrease the area of contact between the lipid and the aqueous phases and favours the H II and L β phases relative to L α phase. This hypothesis is consistent with the effects of chaotropic reagents on the L α-H II phase transition ( Yeagle and Sen (1986) Biochemistry 25, 7518–7522) and on the stability of the lamellar phase of dipalmitoylphosphatidylcholine ( Oku and MacDonald (1983) J. Biol. Chem. 258, 8733–8738).