Membrane complex lipids

Lipid extracted from human hair is similar in composition to scalp lipid [134]. Thus, the bulk of the extractable lipid in hair is free lipid however, cell membrane complex lipid is also partially removed by extraction of hair with lipid solvents or surfactants. In a sense, the scalp serves as a lipid supply system for the hair, with sebum being produced continuously by the sebaceous glands [135]. Sebum production is controlled hormonally by androgens that increase cell proliferation in the sebaceous glands, and this in turn increases sebum production [135,136], although seasonal and even daily variations in the rate of sebum production do occur [137]. 

Light radiation attacks hair proteins, the cell membrane complex hpids, and the hair pigments. The emphasis in this section is on the photochemical degradation of the proteins of hair with some discussion on the degradation of the cell membrane complex lipids and proteins. Later in this chapter, in the discussion on hair pigments, the effects of light on melanins are considered. 

FIGURE 6-15 Schematic representation of the ion permeability modulation for cation-responsive voltammetric sensors based on negatively charged lipid membranes. Complexation of the guest cation to the phospholipid receptors causes an increase of the permeability for the anionic marker ion. (Reproduced with permission from reference 49.)... 

Kauss, H., Swanson, A.L., Arnold, R., and Odzuck, W. (1969) Biosynthesis of Pectic Substances. Localization of enzymes and products in a lipid-membrane complex. Biochim.Biophys.Acta, 192 55-61. 

The intracellular and plasma membranes have a complex structure. The main components of a membrane are lipids (or phospholipids) and different proteins. Lipids are fatlike substances representing the esters of one di- or trivalent alcohol and two aliphatic fatty acid molecules (with 14 to 24 carbon atoms). In phospholipids, phosphoric acid residues, -0-P0(0 )-O-, are located close to the ester links, -C0-0-. The lipid or phospholipid molecules have the form of a compact polar head (the ester and phosphate groups) and two parallel, long nonpolar tails (the hydrocarbon chains of the fatty acids). The polar head is hydrophihc and readily interacts with water the hydrocarbon tails to the... 

J. Uy, M. Tanaka, T. Kishimoto, Y. Mass spectral analysis of complex lipids desorbed directly from lyophilized membranes and cells. Biochem. Biophys. Res. Comm. 1987,142,194-199. 

Liposomes made from pure phosphatidylcholine or containing lipids that are found in the cell membrane complex of wool (e.g. cholesterol) have been used to encapsulate aqueous chlorine solutions in chlorination processes [61,62]. The results showed improvements in... 

Exploration of the use of liposomes in wool processing stems from the similarity that exists between the bilayer structure of the cell membrane complex of wool and that of the liposomes. Merino wool contains about 1% by weight of lipids, these forming the hydrophobic barrier of the cell membrane complex. Cholesterol is one of the main lipid... 

Abstract To understand how membrane-active peptides (MAPs) function in vivo, it is essential to obtain structural information about them in their membrane-bound state. Most biophysical approaches rely on the use of bilayers prepared from synthetic phospholipids, i.e. artificial model membranes. A particularly successful structural method is solid-state NMR, which makes use of macroscopically oriented lipid bilayers to study selectively isotope-labelled peptides. Native biomembranes, however, have a far more complex lipid composition and a significant non-lipidic content (protein and carbohydrate). Model membranes, therefore, are not really adequate to address questions concerning for example the selectivity of these membranolytic peptides against prokaryotic vs eukaryotic cells, their varying activities against different bacterial strains, or other related biological issues. 

Eukaryotic cells have evolved a complex, intracellular membrane organization. This organization is partially achieved by compartmentalization of cellular processes within specialized membrane-bounded organelles. Each organelle has a unique protein and lipid composition. This internal membrane system allows cells to perform two essential functions to sort and deliver fully processed membrane proteins, lipids and carbohydrates to specific intracellular compartments, the plasma membrane and the cell exterior, and to uptake macromolecules from the cell exterior (reviewed in [1,2]). Both processes are highly developed in cells of the nervous system, playing critical roles in the function and even survival of neurons and glia. 

Cerebrosides are major constituents of the membrane of brain cells. They are the simplest glycosphingolipids, serving as model substances for more complex lipids of this kind. Furthermore, they are credited with important properties as receptors for hormones and toxins.29 Schemes 4 13 and 4 14 provide a method for preparing sphingosine and its analogs that can be used for the synthesis of cerebroside compounds. 

The last essential dietary components to which we will refer and which were also discovered through feeding experiments with rats, are certain unsaturated fatty acids identified as linoleic, linolenic, and arachidonic acids by Burr and Burr in 1930. The acids are required for the formation of complex lipids which are essential in membranes for the maintenance of their fluidity (Chapter 9). Deficiencies lead to a dermatitis which does not respond to additional B vitamin supplements or to oleic acid. 

Lipid transfer peptides and proteins occur in eukaryotic and prokaryotic cells. In vitro they possess the ability to transfer phospholipids between lipid membranes. Plant lipid transfer peptides are unspecific in their substrate selectivity. They bind phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, and glycolipids. Some of these peptides have shown antifungal activity in vitro The sequences of lipid transfer proteins and peptides contain 91-95 amino acids, are basic, and have eight cysteine residues forming four disulfide bonds. They do not contain tryptophan residues. About 40% of the sequence adopts a helical structure with helices linked via disulfide bonds. The tertiary structure comprises four a-helices. The three-dimensional structure of a lipid transfer peptide from H. vulgare in complex with palmitate has been solved by NMR. In this structure the fatty acid is caged in a hydrophobic cavity formed by the helices. 

Fats are a remarkably effective form of energy storage. Several classes of complex lipids play important roles in human physiology and are key constituents of biological membranes. 

The fatty acids are important building blocks for more complex lipids. 1 turn to these in this chapter, including the role of fats and oils as energy storehouses and that for other complex lipids in the structure and properties of biological membranes. 

Although my central interest in these complex lipids is the role that they play in organizing the stracture of biological membranes, these complex phospholipids also... 

Complex lipids are core components of biological membranes... 

A bilayer formed from complex lipids, largely glycerophospholipids, forms the core structure of biological membranes. This bilayer forms a barrier to penetration of exogenous molecules into the cellular interior. Proteins penetrate into or through this bilayer. 

Glycerophosphollpid a complex lipid based on glycerol, containing two fatty acids, and a polar headgroup an important constituent of biological membranes. 

Complex lipids, such as neutral fats (triacyl-glycerols), phospholipids, and glycolipids, are synthesized via common reaction pathways. Most of the enzymes involved are associated with the membranes of the smooth endoplasmic reticulum. 

Injury to cell plasma membrane can activate acid sphingomyelinase to break down membrane lipid sphingomyelin and generate the second messenger ceramide, a complex lipid, to initiate the apoptosis (HI). Ceramide, perhaps through intracellular mitogen-activated protein kinases (MAPK), can alter cellular susceptibility to TNF-a, FasL, and ionizing radiation-induced apoptosis (HI, Wll). 

Fig. 5.14. Structure and activation of the heterotrimeric G-proteins. Reception of a signal by the receptor activates the G-protein, which leads to exchange of bound GDP for GTP at the a-sub-unit and to dissociation of the pycomplex. Further transmission of the signal may take place via Ga-GTP or via the Py-complex, which interact with corresponding effector molecnles. The a- and y-subunits are associated with the cell membrane via lipid anchors. Signal reception and signal transmission of the heterotrimeric G-proteins take place in close association with the cell membrane. This point is only partially shown in the fignre.

---