Modulation by subphase pH and ions, of 12-(9-anthroyloxy)stearic acid mobility in phospholipid monolayers. A fluorescence recovery after photobleaching study

Abstract

The mobility of acidic phospholipid monolayers was investigated by means of fluorescence recovery after photobleaching of the 12-(9-anthroyloxy)stearic acid embedded in it. It was shown that for a given fatty acyl chain composition, the mobility in the liquid expanded state is modulated both by the nature and the concentration of the aqueous subphase cations. On NaCl, where dilauroylphosphatidylglycerol and phosphatidylglycerol with methyl-branched fatty acyl chains are in the liquid expanded state, the probe mobility is slower for the branched phospholipid. It is also shown that the probe mobility in monolayers of phosphatidylglycerol extracted from the bacterium Micrococcus luteus membranes, is modulated by cations in the increasing order 1 mM Ca 2+ > 1 M Mg 2+ > 100 mM Na +. On 0.1 M NaCl subphase the mobility of membrane isolated phospholipids varies in the order phosphatidylglycerol < cardiolipin < phosphatidylinositol. The results are interpreted with reference to the “free volume” model of diffusion which also includes a drag force that acts on the head group of the lipid to modulate its mobility.