Negatively charge phospholipid

Activated partial thromboplastin time (aPTT) is a coagulation assay, which measures the time for plasma to clot upon activation by a particulate substance (e.g., kaolin) in the presence of negatively charged phospholipids. 

The survey of over 50 artificial lipid membrane models (pION) in this chapter reveals a new and very promising in vitro GIT model, based on the use of levels of lecithin membrane components higher than those previously reported, the use of negatively charged phospholipid membrane components, pH gradients, and artificial sink conditions. Also, a novel direction is suggested in the search for an ideal in vitro BBB model, based on the salient differences between the properties of the GIT and the BBB. 

For acids, the membrane retention actually increases in the case of egg lecithin, compared to soy lecithin. This may be due to decreased repulsions between the negatively charged sample and negatively charged phospholipid, allowing H-bond-ing and hydrophobic forces to more fully realize in the less negatively charged egg lecithin membranes. The neutral molecules display about the same transport properties in soy and egg lecithin, in line with the absence of direct electrostatic effects. These differences between egg and soy lecithins make soy lecithin the preferred basis for further model development. 

Introducing negative-charge phospholipids to the 2% DOPC at pH 7.4 improved the correlations significantly (models 5.0, 6.0, 7.0, 8.0, 9.0, 10.0). Sink conditions only marginally improved the correlations for the dodecylcarboxylic acid (1.1% DA) and phosphatidic acid (0.6% PA) models (models 6.1 and 7.1). The phospha-tidylglycerol (PG) models (models 9.1 and 10.1) did not correlate well under sink conditions. The modified Chugai model at pH 7.4 performed well (r2 0.60), but was unstable under sink conditions. 

The correct ratio of lipid constituents is important to form stable liposomes. For instance, a reliable liposomal composition for encapsulating aqueous substances may contain molar ratios of lecithin cholesterol negatively charged phospholipid (e.g., phosphatidyl glycerol (PG)) of 0.9 1 0.1. A composition that is typical when an activated phosphatidylethanolamine (PE) derivative is included may contain molar ratios of phosphatidylcholine (PC) cholesterol PG derivatized PE of 8 10 1 1. Another typical composition using a maleimide derivative of PE without PG is PC male-imide-PE cholesterol of 85 15 50 (Friede et al., 1993). In general, to maintain membrane stability, the PE derivative should not exceed a concentration ratio of about l-10mol PE per lOOmol of total lipid. 

The molecular basis of the positive-inside rule is unknown. However, negatively charged phospholipids can control the membrane protein topology, suggesting part of the mechanism (van Klompenburg et al., 1997). 

Similarly comb-like copolymers of vinyl pyrollidone and vinyl alkyl amines were shown [446] to influence the permeability of negatively charged phospholipid liposomes containing encapsulated carboxyfluorescein. At a pH of approximately 7, the copolymers allowed permeability and solute release due to polymer/liposome complex formation and disruption of the phospholipid membrane. 

The photoreduction of AuC14 in the presence of dimyristoyl-L-alpha-phosphati-dyl-DL-glycerol, which is a negatively charged phospholipid, gives rise to Au NPs coated through electrostatic adsorption of a biomolecule, leading to a nanosized model of a biomembrane [148]. 

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... 

Membrane fusion consists of merging two negatively charged phospholipid bilayers, and thus requires overcoming a major energy barrier (Jahn et al., 2003). SNARE proteins represent a family of membrane proteins that are present on opposing membranes destined to fuse. As first proposed by Jahn, Heuser, Rothman and colleagues... 

Lishko VK, Terletskaya YT, Trikash IO (1990) Fusion of negatively charged phospholipid-vesicles by a-latrotoxin. FEBS Letters 266 99-101... 

Stamatatos, L., R. Leventis, M.J. Zucker-mann, and J.R. Silvius. 1988. Interactions of cationic lipid vesicles with negatively charged phospholipid vesicles and biological membranes. Biochemistry 27 3917-3925. 

The negatively charged phospholipid phosphatidylserine is asymmetrically distributed in mammalian cell membranes, primarily on the inner leaflet. Upon exposure to collagen or thrombin, the distribution of phospholipids changes with increasing phosphatidylserine in the external membrane leaf (I). The increased expression of phosphatidylserine on the outer leaflet of the membrane creates a procoagulant surface on which several steps of the coagulation cascade take place. 

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