Packing state in bilayer membranes of diacylphosphatidylcholines with varying acyl chain lengths under high pressures

The bilayer packing states of a series of diacylphosphatidylcholines (CnPC) containing linear saturated acyl chains were examined by a high-pressure fluorescence method. We revealed from the second derivatives of Prodan fluorescence spectra for all bilayer membranes that the Prodan molecules can be distributed into multiple sites in these bilayer membranes and move around the head-group region, depending on the phase state. The hydrophobicity of the PC molecules markedly affected the distribution quantities of the Prodan molecules between the gel and liquid crystalline phases. The distribution of the Prodan molecules into the gel phase decreased with the increasing acyl chain length while that into the liquid crystalline phase conversely increased. The present study suggests that Prodan can sensitively recognize the packing states and strengths in the bilayer membranes and becomes a good packing indicator.