Phospholipid bilayer detergent disruption

When the microencapsulated liposomes are left untreated the lipid bilayer provides a barrier to diffusion through which the entrapped protein does not pass until the liposomes gradually become leaky, primarily due to oxidation of the phospholipid side chains. This mechanism results in a delayed release. Triton or sonic treatment of the microencapsulated liposomes provide pulsed re ease. Since both detergent and sonication disrupt lipid bi ayers, the mechanism by which pulsed release is achieved may be that these stimuli initially disrupt the liposomes and then the lipid reforms around some of the protein solution inside the capsule, possibly in an altered lamellar form alternatively, the treatment could disrupt only the more susceptible liposomes, leading to two phases of release, first from the freed protein and later from protein that remained liposome-entrapped. 

Polymyxin B. Polymyxin antibiotics are cationic compounds that are attracted to negatively charged phospholipids in the bacterial cell membrane. These drugs penetrate and disrupt the architecture and integrity of the surface membrane. Essentially, polymyxins act as detergents that break apart the phospholipid bilayer, which creates gaps in the bacterial cell wall, leading to the subsequent destruction of the bacteria.31... 

Detergents are used to solubilize and study biological membranes and proteins (63-65). Detergents or surfactants disrupt membranes by intercalating into phospholipid bilayers and solubilizing lipids and proteins. Nonionic surfactants are deemed to be milder detergents and do not usually result in protein denaturation. Nonionic surfactants form complexes with membrane proteins that are more or less fixed in the cell membrane (61). 

It is of interest not only to perforate vesicle membranes but also to destroy them after they have served their purpose as transport vehicles, in particular for DNA. Natural vesicles, so-called endosomes, contain about 50% cholesterol. The disruption of such cholesterol-containing lipid bilayers by Triton XI00 or sodium deoxycholate, examples of artificial and natural detergents, results in a leaky membrane at low concentration and in a catastrophic rupture process above the cmc of the amphiphiles. Vesicles made of fluid phospholipid bilayers devoid of cholesterol showed only leakiness under the same conditions. Amphiphiles with a carboxylate end group and a very bulky hydrophobic end (e.g., with two tert. butyl groups) disrupt membranes at pH 5 and have no effect above pH 7 (harpoons). For an example, see Figure 6.5.3. 

Integral proteins are dissolved into the lipid bilayer of the membrane through interactions of the hydrophobic amino acid side chains and fatty acyl groups of phospholipids. In order to remove integral membrane proteins, the membrane must be disrupted by addition of detergents or other chaotropic reagents to solubilize the protein and to prevent aggregation and precipitation of the hydrophobic proteins upon their removal from the membrane. 

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