1-2-linoleoylphosphatidylcholine and 1-2-diarachidonoyl-glycero-3-phosphocholine

Hydrophobic mismatch which is defined as the difference between the lipid hydrophobic thickness and the peptide hydrophobic length is known to be responsible in altering the lipid/protein dynamics. Gramicidin A (gA), a 15 residue β helical peptide which is well recognized to form ion conducting channels in lipid bilayer, may change its structure and function in a hydrophobic mismatched condition. We have performed molecular dynamics simulations of gA dimer in phospholipid bilayers to investigate whether or not the conversion from channel to non-channel form of gA dimer would occur under extreme negative hydrophobic mismatch. By varying the length of lipid bilayers from DLPC (1, 2-Dilauroyl-sn-glycero-3-phosphocholine) to DAPC (1, 2-Diarachidoyl-sn-glycero-3-phosphocholine), a broad range of mismatch was considered from nearly matching to extremely negative. Our simulations revealed that though the ion-channel conformation is retained by gA under a lesser mismatched situation, in extremely negative mismatched situation, in addition to bilayer thinning, the conformation of gA is changed and converted to a non-channel one. Our results demonstrate that although the channel conformation of Gramicidin A is the most stable structure, it is possible for gA to change its conformation from channel to non-channel depending upon the local environment of host bilayers.

Topics: Dimyristoylphosphatidylcholine; Gramicidin; Hydrophobic and Hydrophilic Interactions; Ion Channels; Lipid Bilayers; Molecular Dynamics Simulation; Phosphatidylcholines; Protein Structure, Secondary; Thermodynamics

The echogenic properties of synthetic, phospholipid encapsulated, air-filled microbubbles with various carbon-chain length as ultrasound contrast agents are investigated through the use of a flow-through laboratory ultrasound system. Specifically, we investigate the effect of shell carbon-chain length on the ultrasonic signal for a variety of flow rates. Averaged, integrated backscatter power measurements from the lipid encapsulated agents are benchmarked against those of Albunex (Albunex is a registered trademark of Molecular Biosystems, Inc., San Diego, CA), a commercially available, air-filled protein microbubbles contrast agent, approved for clinical use in echocardiography in the United States by the Food and Drug Administration. We find that the lipid encapsulated agents sustain less damage leading to gas dissolution or particle destruction as compared to Albunex in the slow-flow studies performed. The carbon-chain length of the encapsulating lipid molecule is shown not to observably affect the backscattered amplitude of ultrasound at flow velocities exceeding 7 mm/s.

Topics: Contrast Media; Particle Size; Phosphatidylcholines; Ultrasonics

Liposomes containing dilinoleoyl lecithin (di-18(2)PC) and diarachidonyl lecithin (di-20(4)PC) were peroxidized with Fe++/ascorbate. Lipidperoxidation was measured as generated malondialdehyde, the disappearance of polyunsaturated fatty acids, conjugated diene formation and chemiluminescense. It was found that di-20(4)PC was oxidized rapidly, while in the same time period hardly any oxidation of di-18(2)PC took place. Incorporation of different lipid classes into the di-20(4)PC liposomes influenced the peroxidation for each lipid in a characteristic way. Phosphatidylethanolamine stimulated the formation of fluorescent chromolipids. The possible meaning of these reactions in human pathology is discussed.

Topics: Aldehydes; Kinetics; Lipid Peroxides; Liposomes; Luminescent Measurements; Models, Biological; Oxidation-Reduction; Phosphatidylcholines; Structure-Activity Relationship