Sphingomyelin multiple phase behavior as revealed by multinuclear magnetic resonance spectroscopy.

31P and 13C nuclear magnetic resonance (NMR) spectra are employed to study the phase behavior of bovine brain sphingomyelin as a function of temperature. The 31P NMR data suggest that, while at low temperatures sphingomyelin can form a lamellar phase, at physiological temperatures and higher the lamellar phase is unstable, and a new phase, best described as a hexagonal phase, is formed. Egg phosphatidylcholine is suggested to play an important role in stabilizing bilayers in natural membranes. Cholesterol also exhibits a sphingomyelin bilayer-stabilizing ability. The 13C NMR spectra suggest a gelling of the hydrocarbon chains of sphingomyelin at low temperature. Thus, bovine brain sphingomyelin undergoes both a gel to liquid-crystalline phase transition and a lamellar to nonlamellar transition.