Organization of chlorophyll a in bilayer membranes. The chlorophyll a/dimyristoylphosphatidylcholine system.
In order to investigate the relative importance of the hydrophobic and headgroup interactions of chlorophyll a in phospholipid bilayers, we have carried out differential scanning calorimetry (DSC) and deuterium (2H) and phosphorus (31P) nuclear magnetic resonance (NMR) experiments on the multilamellar system of chlorophyll a in dimyristoylphosphatidylcholine (DMPC). Compared to the phytol chain of chlorophyll and the previously reported distearoylphosphatidylcholine (DSPC), the acyl chains of DMPC are shorter in length by three and four carbons, respectively. A lowering in the phase-transition temperature was observed for the DMPC multilayers in the presence of chlorophyll a in the DSC thermograms and in the 31P chemical shift anisotropy measurements. These results, together with data on hydrophobic interactions as measured by 2H-NMR and on headgroup interactions as evidenced from 31P-NMR, suggest a phase diagram for the chlorophyll a/DMPC system in which phase separation readily occurs between a chlorophyll-rich compound phase and a chlorophyll-poor phospholipid phase. Compound formation appears to be important in the stabilization of chlorophyll a in bilayers with shorter chains.
D002152:Calorimetry, Differential Scanning; D002734:Chlorophyll; D000077194:Chlorophyll A; D004134:Dimyristoylphosphatidylcholine; D008051:Lipid Bilayers; D009682:Magnetic Resonance Spectroscopy; D013696:Temperature; D013816:Thermodynamics
D008051:Lipid Bilayers; D002734:Chlorophyll; D004134:Dimyristoylphosphatidylcholine; D000077194:Chlorophyll A