Long-chain phospholipids

Several monounsaturated phospholipid fatty acids exist in nature, but few cases are known of very long-chain monounsaturated acids longer than 22 carbons. However, marine sponges are unusual in that they have very long-chain fatty acids in their phospholipids. Sponges have provided the most interesting examples of long-chain phospholipid fatty acids since... 

We have now extended these studies to synthetic phospholipids that contain short chain fatty acyl groups and which are water soluble, such as dibutyryl and dihexanoyl phosphatidylcholine (PC). These phospholipids are monomeric below their critical micelle concentration (cmc), yet activate the enzyme. In order to carry out kinetic studies, the long chain phospholipid substrate must generally be solubilized by a detergent such as Triton X-100 which serves as an inert matrix. Further understanding of the mechanism of the activation by short-chain phospholipids requires first a quantitation of the solubilization of these compounds by detergent ... 

N. E. Gabriel, N.V. Agman, and M. F. Roberts. Enzymatic-hydrolysis of short-chain lecithin long-chain phospholipid unilamellar vesicles sensitivity of phospholipases to matrix phase state. Biochemistry, 1987, 26, 7409-7418. 

The extent of the blocking effect apparently depends on the driving force for ET. When the driving force is small (e.g., AE° 100 mV for Ru(CN>6 and ZnPor+), the formation of any long-chain phospholipid monolayer (i.e, from C-10 to C-20) results in a ET rate below the lower limit for SECM measurements. This shows that the density of the possible defects in the monolayer is too low to produce detectable feedback current under experimental condition of Ref. 26. 

Topical pancreatic lipase substrates like tributyrin and triolein emulsions are hydrolyzed by carboxylester lipase in the presence of bile salt but slowly—at a rate lower than 3% and 0.5%, respectively, of that observed with the lipase-colipase complex. On the other hand, the positional specificity is not restricted all three sn positions of triglycerides can be split by the carboxylester lipase. While long-chain phospholipids are resistant, short-chain phospholipids are readily attacked by carboxylester lipase [40]. The low substrate specificity of carboxylester lipase makes possible an essential role for this enzyme in the hydrolysis of triglycerides containing certain esterified polyunsaturated fatty acids, such as eicosapentaenoic, arachidonic, or linoleic acids [41], and which may be resistant to attack by pancreas lipase (see p. 190). 

Figure 7.55. IR bands used to monitor phase behavior of long-chain phospholipids. These bands, which are marked on spectrum, represent methyiene antisymmetric (of-) and symmetric (cf-F) C-H stretching, scissoring (5), and wagging (w) modes. Spectra shown are of fully hydrated diCIBPC the gel phase at -19° (solid curves) and in liquid-crystalline phase at 58° (dotted curves). Types of methylene-hydrogen motion associated with bands of interest are depicted. Reprinted, by permission, from R. G. Snyder, G. L. Liang, H. L. Strauss, and R. Mendelsohn, Biophys. J. 71,3186 (1996), p. 3188, Fig. 1. Copyright 1996 Biophysical Society.

A molecular variation of plasma membrane has been reported by Puccia et al. Reduction of total lipids (XL) content and significant variations of triglyceride (TG) and phospholipids (PL) fractions were observed as a consequence of exposure of C. intestinalis ovaries to TBTCl solutions. In particular, an evident TG decrease and a PL increase were observed, which probably provoked an increment in membrane fluidity, because of the high concentration of long chain fatty acids and, as a consequence, PL. This could be a cell-adaptive standing mechanism toward the pollutants, as observed in Saccharomyces cerevisiae. Also the increase in the content of the polyunsaturated fatty acids (PUPA), important in the synthesis of compounds such as prostaglandin which are present in the ovary in a stress situation, was probably a consequence of a defense mechanism to the stress provoked by the presence of TBTCl. 

Painted BLMs were made of a solntion of the desired phospholipid in a long-chain alkane (n-decane or hexadecane) or sqnalene [160], Again, a Teflon cnvette was separated into two compartments by a septnm with an orifice 0.8-3 mm in diameter. The orifice was... 

Plasma lipids consist of triacylglycerols (16%), phospholipids (30%), cholesterol (14%), and cholesteryl esters (36%) and a much smaller fraction of unesteri-fied long-chain fatty acids (free fatty acids) (4%). This latter fraction, the free fatty acids (FFA), is metaboh-cally the most active of the plasma hpids. 

The cell walls of mycobacteria contain three structures peptidoglycan, an arabinogalactan polysaccharide and long chain hydroxy fatty acids (mycolic acids) which are all covalently linked. Additional non-covalently attached lipid components found in the wall include glycolipids, various phospholipids and waxes. The lipid-rich nature of the mycobacterial wall is responsible for the characteristic acid-fastness on staining and serves as a penetration barrier to many antibiotics. Isoniazid and ethambutol have long been known as specific antimycobacterial agents but their mechanisms of action have only recently become more clearly understood. 

Biomembranes mainly consists of phospholipid matrices, and the major component is phosphorylcholines (PC). PC is an amphiphile consisting of hydrophilic headgroup and hydrophobic long chains. In view of the amphiphilic feature of PC, we can divide hydrated lipid bilayers into the three zones, I, II, and III. The zone model, which has been used in a recent NMR study of DD [46-48], is illustrated in Fig. 2. 

Hepatic steatosis usually is a result of excessive administration of carbohydrates and/or lipids, but deficiencies of carnitine, choline, and essential fatty acids also may contribute. Hepatic steatosis can be minimized or reversed by avoiding overfeeding, especially from dextrose and lipids.35,38 Carnitine is an important amine that transports long-chain triglycerides into the mitochondria for oxidation, but carnitine deficiency in adults is extremely rare and is mostly a problem in premature infants and patients receiving chronic dialysis. Choline is an essential amine required for synthesis of cell membrane components such as phospholipids. Although a true choline deficiency is rare, preliminary studies of choline supplementation to adult patients PN caused reversal of steatosis. 

SCDs are a family of microsomal Fe-based metalloenzymes. They act on long-chain saturated acyl CoAs and introduce a ds-double bond at the C-9 or C-10 position. For example, SCDs convert stearic acid into oleic acid, and palmitic acid into palmitoleic acid. Monounsaturated FAs constitute a major component of TGs, cholesteryl esters, and phospholipids. The reaction requires molecular 02 and NADH and generates H20 in the process [3,4]. 

The hydrophobic tail is provided by long-chain fatty acids attached to a glycerol backbone. The head group contains oxygen and may be positively charged or neutral. The name of the phospholipid is dictated by the head group. The head and tail are attached through a phosphate diester. 

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