Phosphatidylcholine/7-ketocholesterol Interactions: II. Effect of Phospholipid Acyl Chain Length in Gel State Bilayers

Abstract

Oxygenated sterol compounds have recently been shown to interact in a manner different from that of cholesterol with phospholipid bilayers and red blood cell membranes. Part of the difference between mixtures of dipalmitoylphosphatidylcholine with cholesterol and with 7-ketocholesterol is in the number of gel state lamellar phases formed at low sterol concentrations [W. Tamura-Lis, L. J. Lis and J. M. Collins, Mol. Cryst. Liq. Cryst, 132, 209-219 (1986)]. In this report, we examine mixtures of 7-ketocholesterol and distearoylphosphatidylcholine in water at 25°C using X-ray diffraction. Two gel state lamellar phases with different bilayer repeat spacings are observed at low sterol concentrations (1:19, 7-ketocholesterol/DSPC). These results indicate a difference in the miscibility of cholesterol and 7-ketocholesterol in gel state bilayers made from phosphatidylcholines of different acyl chain lengths. These results may have implications for the composition of domains in cell membranes.