Hardeners, lipids

Cuticle. The cuticle of adult nematodes is relatively impermeable and is composed primarily of a complex of several proteins. These proteins include collagens, fibroids, elastoids, and keratoids, possibly hardened by tanning with pol3rphenols or quinones. Sometimes lipide materials are also present (8, 10y 52). When such lipide materials are present on the adult cuticle, they probably take the form of hydroxy fatty acids or esters of fatty acids with monohydroxy alcohols. Such materials may form ring compounds. Regardless of the exact chemical nature, the lipides are unquestionably one of the chief barriers to permeability. These materials are commonly difficult to demon-... 

Inclusion of other molecules of irregular shape within membranes also lowers Tm. However, a molecule of cholesterol can pack into a bilayer with a cross-sectional area of 0.39 nm2, just equal to that of two hydrocarbon chains.49 It tends to harden membranes above Tm but increases mobility of hydrocarbon chains below Tm.97 -100 A complex of cholesterol and phosphatidylcholine may form a separate phase within the membrane.101102 The ether-linked plasmalogens may account for over 30% of the phosphoglycerides of the white matter of the brain and of heart and ether linked phospholipids are the major lipids of many anaerobic bacteria.103 Their Tm values are a few degrees higher than those of the corresponding acyl phospholipids.104... 

Many changes in the lipid composition of the plasma membrane have been associated with hardening (Lynch Steponkus, 1987). In rye (cv. Puma) an increase of the total lipid content has been measured during hardening (Cloutier, 1987). Free sterols increased while steryl-glycoside and acylated steryl-glycoside decreased. In addition the phospholipid contents of the plasma membrane increased. 

Cloutier, Y. (1987). Lipid and protein changes in cold- and drought-hardened cereals. Phytoprotection 68, 87-96. 

Williams-Aziz SL, Hartline CB, Harden EA, et al. Comparative activities of lipid esters of cidofovir and cyclic cidofovir against replication of herpesviruses in vitro. Antimicrob Agents Chemother. 2005 49 3724-3733. 

Lipids are constituents of plants and animals that are characteristically insoluble in water. Fats and oils are lipids that are triesters formed by reaction of the triol glycerol with long-chain saturated or unsaturated acids called fatty acids. The common acids in fats and oils have an even number of carbons (for example, stearic acid has 18 carbons), and, if unsaturated (for example, oleic acid), they have the Z configuration (Table 15.1 lists the fatty acids, with their common names). Hydrogenation of oils, which have a high percentage of unsaturated acids, converts them to solid fats in a process called hardening. 

Fig. 57.—Effect of lipids on formation of complexes with wheat starch (GMO, glyceryl monooleate GML, glyceryl monolinoleate GMS, glyceryl monooctadecanoate SL, soy lecithin HPF, hardened peanut fat SO, soy oil.741 ...

Fig. 58.—Effect of lipids on the formation of starch complexes with potato starch. (HPFex, hardened extracted peanut fat other notation as in Fig. 57).749...

Figure 2.4 Summed BDE congener concentrations ( ig/kg lipid weight) in each pool of blood serum analysed by the respective mean age (in years) of donors in each pool. Each data point represents a pool of up to 100 blood samples. (Reproduced by permission from Environmental Science and Technology, Higher Accumulation of Polybrominated Diphenyl Ethers In Infants Than in Adults, by Toms, L.-M. L., Harden, F., Paepke, O., Ryan, J.)., Hobson, P., Mueller, J. F., 42(19), 2510-2515. Copyright 2008 American Chemical Society)...

The carbonyl compounds formed due to autoxidation of lipids and in catabolic processes postmortem in muscles, or introduced with wood smoke, can bring about undesirable effects by interacting with a.a. residues. On the other hand, some carbonyl compounds are used intentionally to modify the proteins. Formaldehyde can harden the collagen dope in the manufacturing of sausage casings, protect fodder meals against deamination by the rumen microflora, and bind immobilized enzymes on supports. 

The classic profile of the stroke victim is one with high blood pressure, evidence of arterial hardening, and high levels of cholesterol and other lipid substances in the blood. Diabetes or gout are frequently present as is a long history of smoking. All of these factors have been found to compound the risk of morbidity and mortality greatly. 

Many suppository bases are made up of various acylglycerols. Hardening of suppositories is considered to result from various phase transitions, crystallization, and transesterification reactions in these lipids. The DSC thermograms of a semisynthetic, hard base triglyceride shown in Fig. 177 indicate that a polymorphc phase transition occurred during storage.709... 

While dietary saturated FA have only a slight effect on the FA in the samples, trans-FA can have a considerable influence. With a diet containing 5.5 g trans-FA daily in the form of hardened fats, after 16 days the trans-FA increased up to 10% at the expense of some proportion of oleic acid in the neutral lipids. Less trans-FA are transferred into the phospholipid fraction than into the TAG fraction (Kaufmann and Mankel, 1967). From rapeseed oil (which contains erucic acid), the erucic acid is transferred into the egg (Biedermann et al., 1971). In addition to the increase in C,82 acid in egg Upids, the physical characteristics change, thus increasing the tendency toward oxidation. 

At Stanford, Harden M. McConnell developed a new technique, called spin labelling, based upon EPR spectroscopy. While carbon-centered free radicals are extremely reactive and short-lived, radical oxides of nitrogen, such as NO and NO2, are moderately stable. McConnell noted that nitroxyl radicals (RR N-O) are extremely stable if R and R are tertiary and can be chemically attached to biological molecules of interest. In 1965, he published the concept of spin labeling and, in 1966, demonstrated that a spin-labelled substrate added to a-chymotrypsin forms a covalent enzyme-substrate complex. The EPR signal was quite broad suggesting restricted motion consistent with Koshland s induced-fit model. In 1971, McConnell published a smdy in which spin labelling indicated flip-flop motions of lipids in cell membranes. This was the start of dynamic smdies of cell membranes. 

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