Membrane lipids, classifications

AC ADME ANS AUC BA/BE BBB BBM BBLM BCS BLM BSA CE CHO CMC CPC CPZ CTAB CV DA DOPC DPPC DPPH aminocoumarin absorption, distribution, metabolism, excretion anilinonaphthalenesulfonic acid area under the curve bioavailability-bioequivalence blood-brain barrier brush-border membrane brush-border lipid membrane biopharmaceutics classification system black lipid membrane bovine serum albumin capillary electrophoresis caroboxaldehyde critical micelle concentration centrifugal partition chromatography chlorpromazine cetyltrimethylammonium bromide cyclic votammetry dodecylcarboxylic acid dioleylphosphatidylcholine dipalmitoylphosphatidylcholine diphenylpicrylhydrazyl... 

The amino acid composition of several membrane proteins, whether structural or total, show about equal molar percentages of polar and nonpolar residues (Table 1). In the classification adopted, an ability to undergo polar interactions, whether ionic or other, was the sole consideration. There is no indication from these data to support a current theory (Griddle et al., 1962) that membrane lipid/protein interactions are mainly hydrophobic unless one insists on ignoring the existence of polar bonds other than strictly ionic, hydrogen bonds for example, the occurrence of which has been thoroughly documented both in relation to proteins and polar lipids (see Section III, G, 1, b). 

Lipids are substances that are considered to be essential for cell functioning all cells contain lipids, hence lipids must be primary metabolites However, the spectrum of lipids produced by various species can differ very markedly indeed the lipid spectrum of a species can help identify that species.= Furthermore, the study of mutants with altered lipid compositions has shown that some individual lipids can be lost from plants without any apparent loss of short-term fitness. This suggests that some individual lipids are more like NPs and can be lost without a short-term loss of fitness. But clearly, cells need lipid-rich membranes hence, some lipids are essential for life. So, lipids as a group would have to be classified by KosseTs definition of primary metabolites but some individual lipids wouid be classified as secondary (equivalent to NPs). The way to resolve this contradiction is to abandon KosseTs classification, as will be argued in more detail later, but first another instructive example. 

Mammalian stratum comeum (SC) consists of highly comified cells embedded in a matrix of lipid bilayers (Matoltsy, 1976). These extracellular lipids are arranged in the form of multiple lamellae that are believed to constitute the major barrier to percutaneous penetration (Michaels et al., 1975 Elias, 1983). As discussed, the SC lipid membranes are made up predominantly of ceramides, cholesterol, free fatty acids, cholesteryl sulfate, and small amounts of some less well-defined nonpolar components (Gray et al., 1982 Yardley and Summerly, 1981). Six groups of ceramides have been characterized in porcine SC, as shown in Fig. 4 (Wertz et al., 1983). This classification was based on the polarity of the ceramides, with ceramide 1 being the least polar. 

Improved bioavailability. More than 40% of the NCEs (new chemical entity) discovered have good membrane permeability but poor aqueous solubility (i.e.. Biopharmaceutics Classification System II). By formulating the NCE in solution inside a Softgel (e.g., lipid based) or in micro/nano emulsion, the solubility and hence the bioavailability of the compound may be improved. ... 

The structural classification of synthetic ion channels and pores differentiates between (macro)molecules and different classes of supramolecules [2]. Unimolec-ular synthetic ion channels and pores are usually hollow, often helical (macro)mol-ecules that are long enough to span common lipid bilayer membranes (2-4 nm). 

A third classification of membrane proteins consists of lipid-anchored proteins bound to the iimer or outer surface of the membrane. The glycophosphatidylinosi-tolglycan (GPI) anchor is a covalently attached lipid that anchors proteins to the... 

I 12 FRAC Mode of Action Classification and Resistance Risk of Fungicides Table 12.11 Group F Fungicides interfering with lipid and membrane synthesis, cell wall deposition. 

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