Interaction of gramicidin with lysophosphatidylcholine as revealed by calorimetry and fluorescence spectroscopy.

Abstract

The effect of the interaction of gramicidin (GA) with lysophosphatidylcholine (LPC) on the change in lipid structure upon heat incubation was revealed by differential scanning calorimetry (DSC) and fluorescence spectroscopy. DSC showed a large endothermic transition in both pure LPC micelles and GA-containing LPC micelles after prolonged heat incubation at 70 degrees C. To elucidate this behavior, fluorescence spectra of 1-anilinonaphthalene-8-sulfonate embedded in LPC micelles were measured. About 40% of the resultant LPC micelles was found to be transformed into the interdigitated gel structures after prolonged heat incubation. On the other hand, intrinsic fluorescence spectra of GA-containing LPC micelles caused a blue-shift of the emission maxima with incubation time, suggesting that tryptophans near the C-terminus of GA moved into a more apolar environment. In addition, GA-containing LPC micelles caused quenching of fluorescence with incubation time, due to the interaction between GA molecules. To determine the location of GA in LPC membranes, surface pressure was measured using the mixed monolayers composed of GA and LPC. The result suggests that GA molecule is localized by interdigitating the C-terminal part of adjacent to acyl chain of LPC.