Phospholipid transmembrane asymmetry

Rauch, C. and Farge, R, 2000, Endocytosis switch controlled by transmembrane osmotic pressure and phospholipid number asymmetry. Biophys. J., 78 3036-3047. 

Methods used to demonstrate the existence of membrane phospholipid asymmetry, such as chemical labelling and susceptibility to hydrolysis or modification by phospholipases and other enzymes, are rmsuitable for dynamic studies because the rates of chemical and biochemical reactions are of a different order compared to the transmembrane translocahon of the phospholipids. Indirect methods have therefore been developed to measure the translocation rate which are consequent on the loss of membrane phospholipid asymmetry. Thus time scales appropriate to rates of lipid scrambling under resting conditions or when the forces preserving the asymmetric phospholipid distribution are disturbed can be monitored. Generally the methods rely on detecting the appearance of phosphatidylserine on the surface of cells. Methods of demonstrating Upid translocation in mammalian cells has been the subject of a recent review (Bevers etal., 1999). 

The biological function of lipid asymmetry and of proteins involved in the transmembrane traffic of lipids is multiple. Rapid reorientation of phospholipids in ery-... 

Wu, G. and Hubbel, W.L., 1993, Phospholipid asymmetry and transmembrane diffusion in photoreceptor disc membranes. Biochemistry, 32 879-888. 

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