Spontaneous Transfer of Sphingomyelin between Phospholipid Bilayers

The half-time of spontaneous transfer of pyrenelabeled and ³H-labeled sphingomyelin has been determined as a function of temperature in several matrix lipids. Data obtained by using the two labels are in good agreement. Transfer half-times from liquid-crystalline phase matrix lipids are about 2 orders of magnitude shorter than the half-times obtained in gel-phase systems; however, transfer half-times are not markedly dependent on the molecular species of matrix lipid. The small half-times of transfer seen below 30 °C in 1-palmitoyl-2-oleoylphosphatidylcholine suggest that a gel phase rich in sphingomyelin may exist in this system even at low sphingomyelin concentrations.