Phospholipids 22 production

Prostaglandins, one of the most important epithelial growth factors, inhibit gastric acid secretion and have numerous mucosal protective effects, the most important of which include the stimulation of both mucus and phospholipid production, promotion of bicarbonate secretion, and increased mucosal cell turnover. Damage to the mucosal defense system is the primary method by which HP or NSAIDs cause peptic ulcers. 

Our laboratory has been studying the kinetics (1) and mechanism of action (2) of phospholipase A2 which catalyzes the hydrolysis of the fatty acyl chain in the sn-2 position of phospholipids to give the 1-acyl lyso-phospholipid product ... 

A2 in mixed phospholipid systems and the kinetics and migration of the acyl and phosphorus group of the lyso-phospholipid products. 

Depending on the type and efficiency of the extraction equipment, the acetone/ crude lecithin ratio necessary to achieve a 95% phospholipid product is 10-20 1 (v/v). In batch extraction, the tank is charged with acetone prior to crude lecithin... 

Greenberg AJ, Trevor AJ, Johnson DA, Loh HH (1979) Immunochemical studies of phospholipids production of antibodies to triphosphoinositide. Mol Immunol 16 193-196 Gross PR, Katz SA, Samitz MH (1968) Sensitization of guinea pigs to chromium salts. J Invest Dermatol 50 424-427... 

Khaselev, N. and Murphy, R.C. (2000) Structural characterization of oxidized phospholipid products derived from arachidonate-containing plasmenyl glycerophosphocholine. J. Lipid Res. 41, 564-572. 

The phospholipid breakdown product of this reaction, lysoleeithin, acts as a detergent and dissolves the membranes of red blood cells, causing them to rupture. Indian cobras kill several thousand people each year. 

Eicosanoids, so named because they are all derived from 20-carbon fatty acids, are ubiquitous breakdown products of phospholipids. In response to appropriate stimuli, cells activate the breakdown of selected phospholipids (Figure 25.27). Phospholipase Ag (Chapter 8) selectively cleaves fatty acids from the C-2 position of phospholipids. Often these are unsaturated fatty acids, among which is arachidonic acid. Arachidonic acid may also be released from phospholipids by the combined actions of phospholipase C (which yields diacyl-glycerols) and diacylglycerol lipase (which releases fatty acids). 

Phospholipase D is widely distributed in bacteria, fungi, plants and animals, and is present in almost all mammalian cells [3]. In mammals, it occurs as alternatively spliced products of two genes (PLD1 andPLD2) (Fig. 3). Most mammalian cells express different levels of both isoforms. Both PLD1 and PLD2 have four conserved sequences (I-IV), and sequences I and IV contain the HXKX4D (HKD) motif that is characteristic of the PLD superfamily, which includes bacterial endonucleases, phospholipid synthases, viral envelope... 

A large number of combinations are theoretically possible and a lot of these structures are actually used in practice. We know that nature makes use of this variety, e.g., to form cell membranes by phospholipids. However, in daily practice the pool of hydrophobic raw material for the production of anionic phosphorus-containing surfactants is survey able. 

In the case of prothrombin and related clotting factors, interruption of the vitamin K cycle leads to the production of nonfunctional, undercarboxylated proteins, which are duly exported from hepatocytes into blood (Thijssen 1995). They are nonfunctional because there is a requirement for the additional carboxyl residues in the clotting process. Ionized carboxyl groups can establish links with negatively charged sites on neighboring phospholipid molecules of cell surfaces via calcium bridges. 

U shape. This has profound significance on molecular packing in membranes and on the positions occupied by fatty acids in more complex molecules such as phospholipids. Trans double bonds alter these spatial relationships. Trans fatty acids are present in certain foods, arising as a by-product of the samration of fatty acids during hydrogenation, or hardening, of natural oils in the manufacture of margarine. An additional small... 

Figure 25-4. Metabolic fate of very low density lipoproteins (VLDL) and production of low-density lipoproteins (LDL). (A, apolipoprotein A B-100, apolipoprotein B-100 , apolipoprotein C E, apolipoprotein E HDL, high-density lipoprotein TG, triacylglycerol IDL, intermediate-density lipoprotein C, cholesterol and cholesteryl ester P, phospholipid.) Only the predominant lipids are shown. It is possible that some IDL is also metabolized via the LRP.

The second type of fatty liver is usually due to a metabolic block in the production of plasma lipoproteins, thus allowing triacylglycerol to accumulate. Theoretically, the lesion may be due to (1) a block in apolipoprotein synthesis, (2) a block in the synthesis of the lipoprotein from lipid and apolipoprotein, (3) a failure in provision of phospholipids that are found in lipoproteins, or (4) a failure in the secretory mechanism itself. 

The intrinsic pathway (Figure 51-1) involves factors XII, XI, IX, VIII, and X as well as prekallikrein, high-molecular-weight (HMW) kininogen, Ca, and platelet phospholipids. It results in the production of factor Xa (by convention, activated clotting factors are referred to by use of the suffix a). 

For cells to carry out their functions, glucose and other nutrients must be brought in, and urea and other waste products must be expelled. This would be an impossible task if cell membranes were composed only of phospholipids. Farge protein molecules act as molecular gates through the membranes (see Chapter 13 for the structures of proteins). These proteins are embedded in the bilayers but protrude into the surrounding water and/or into the cell interiors, as Figure 12-19 indicates. 

In media selective for enterobacteria a surface-active agent is the main selector, whereas in staphylococcal medium sodium and lithium chlorides are the selectors staphylococci are tolerant of salt concentrations to around 7.5%. Mannitol salt, Baird-Parker (BP) and Vogel-Johnson (VJ) media are three examples of selective staphyloccocal media. Beside salt concentration the other principles are the use of a selective carbon source, mannitol or sodium pyruvate together with a buffer plus acid-base indicator for visualizing metabolic activity and, by inference, growth. BP medium also contains egg yolk the lecithin (phospholipid) in this is hydrolysed by staphylococcal (esterase) activity so that organisms are surrounded by a cleared zone in the otherwise opaque medium. The United States Pharmacopeia (1990) includes a test for staphylococci in pharmaceutical products, whereas the British Pharmacopoeia (1993) does not. 

In addition to phenolic substances, there are other components present in foods which have no antioxidant activity of their own, but which increase that of phenolic antioxidants. They are called synergists, and they should be accounted for in any discussion of antioxidant activity. Polyvalent organic acids, amino acids, phospholipids (lecithin) and various chelating agents belong to this group. Proteins may modify the efficiency of antioxidants as they react with the reaction products of both antioxidants and synergists. 

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