Phosphatidylcholine electrical charge

Scherer, P. G. and Seelig, J. (1989). Electric charge effects on phospholipid head-groups. Phosphatidylcholine in mixtures with cationic and anionic amphiphiles, Biochem., 28, 7720-7728. 

Glycerophospholipids differ in the structure of their head group common gycerophospholipids are phosphatidylethanolamine and phosphatidylcholine. The polar heads of the gycerophospholipids carry electric charges at pH near 7. 

Zwitterion A charged molecule displaying one positive and one negative charge (the net electric charge is nuU). Phosphatidylcholine is a zwitterionic lipid. 

In the previous two sections we discussed the electrodeformation and electroporation of vesicles made of single-component membranes in water. In this section, we consider the effect of salt present in the solutions. The membrane response discussed above was based on data accumulated for vesicles made of phosphatidylcholines (PCs), the most abundant fraction of lipids in mammahan cells. PC membranes are neutral and predominantly located in the outer leaflet of the plasma membrane. The inner leaflet, as well as the bilayer of bacterial membranes, is rich in charged lipids. This raises the question as to whether the presence of such charged lipids would influence the vesicle behavior in electric fields. Cholesterol is also present at a large fraction in mammalian cell membranes. It is extensively involved in the dynamics and stability of raft-hke domains in membranes [120]. In this section, apart from considering the response of vesicles in salt solutions, we describe aspects of the vesicle behavior of fluid-phase vesicles when two types of membrane inclusions are introduced, namely cholesterol and charged lipids. 

The distribution of the lipids between the inner and outer leaflet of a biological membrane is asymmetric, with the outer surface being enriched in phosphatidylcholine (PC) and the inner, cytosolic surface in phos-phatidylethanolamine (PE) and phosphatidylserine (PS). As a result, the outer lipid membrane surface is electrically neutral and the inner negatively charged. Spontaneous randomization (flip-flop) of zwitterionic lipids between the two leaflets is extremely slow. Specific transport proteins, belonging to the adenosine triphosphate (ATP) binding cassette, further maintain lipid asymmetry. Lipid asymmetry may play a role for the proper orientation of membrane proteins. 

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