Lipid chemical structure

Types of lipidations Chemical structures of lipids modifications Biological lipidated processes catalysed by Modification sites Reversibility Cell localizations of lipidated proteins Protein examples... 

Thus, although our analysis is preliminary, the differences that neonates detect and respond to behaviorally could very well be due to differences in relative quantities of constituents rather than their presence or absence. It is interesting that, even though B. constrictor and C, v. viridis are relatively distant taxonomically and live in vastly different habitats, there has been surprising conservativism in skin lipid structure during their evolution. It is possible that skin lipid chemical structure has remained relatively constant to maintain its apparent primary function, controlling CWL (Roberts and Lillywhite, 1980 Landmann, 1979, 1980), and that lesser changes have occurred to enhance pheromonal functions or effects in taxa where necessary selective pressures have existed. 

With respect to the carrier mechanism, the phenomenology of the carrier transport of ions is discussed in terms of the criteria and kinetic scheme for the carrier mechanism the molecular structure of the Valinomycin-potassium ion complex is considered in terms of the polar core wherein the ion resides and comparison is made to the Enniatin B complexation of ions it is seen again that anion vs cation selectivity is the result of chemical structure and conformation lipid proximity and polar component of the polar core are discussed relative to monovalent vs multivalent cation selectivity and the dramatic monovalent cation selectivity of Valinomycin is demonstrated to be the result of the conformational energetics of forming polar cores of sizes suitable for different sized monovalent cations. 

Because of their very complex chemical structures and heterogeneity, melanins are difficult to extract, separate, and characterize from tissues. Eumelanins are insoluble in water and organic solvents. They can be extracted from tissues with strong chemicals that are capable of removing lipids, proteins, and other tissue components but also lead to the formation of degradation products. Enzymatic procedures were developed for the isolation of eumelanins from mammalian hair and irises. The first step is sequential digestion with protease, proteinase K, and papaine in the presence... 

Tea leaf, in common with all plant leaf matter, contains the full complement of genetic material, enzymes, biochemical intermediates, carbohydrates, protein, lipids, and structural elements normally associated with plant growth and photosynthesis. In addition, tea leaf is distinguished by its remarkable content of methylxathines and polyphenols. These two groups of compounds are predominantly responsible for those unique properties of tea that account for its popularity as a beverage. It must be noted that the chemical composition of tea leaf varies with climatic condi-... 

Owing to their chemical structure, carotenes as polyterpenoids are hydrophobic in nature (Britton et al., 2004). Therefore, as it might be expected, the carotenes are bound within the hydrophobic core of the lipid membranes. Polar carotenoids, with the molecules terminated on one or two sides with the oxygen-bearing substitutes, also bind to the lipid bilayer in such a way that the chromophore, constituted by the polyene backbone is embedded in the hydrophobic core of the membrane. There are several lines of evidence for such a localization of carotenoids with respect to the lipid bilayers. 

Carotenoid molecules incorporated into the lipid membranes considerably interfere with both the structural and the dynamic membrane properties. Both effects are directly related to the chemical structure of carotenoid molecules. Importantly, it is the rigid, rod-like backbone of the carotenoids,... 

Fig. 8 Immobilization of urokinase on the surfaces of islet cells, (a) Surface modification (/) chemical structure of ssDNA-PEG-lipid, and (2) ssDNA-PEG-lipid anchoring to the cell membrane. (b) Introduction of a complementary ssDNA onto urokinase, which was first modified with a madeimide group by a cross-linker, EMCS. (c) Urokinase-immobilization through DNA...

Figure 7.7 Structure of a generalized LPS molecule. LPS constitutes the major structural component of the outer membrane of Gram-negative bacteria. Although LPSs of different Gram-negative organisms differ in their chemical structure, each consists of a complex polysaccharide component, linked to a lipid component. Refer to text for specific details...

Figure 5. Chemical structures of main lipids of purple membranes from Halobacterium salinarium S9 phosphatidylglycerophosphate (PGP), phosphatidylglycerol (PG) and glycolipid sulfate (GLS).

Fig. 2.—Chemical structure of lipid A of the Escherichia coli Re mutant strain F515. The hydroxyl group at position 6 constitutes the attachment site of Kdo. The numbers in circles indicate the number of carbon atoms present in the fatty acyl chains. The 14 0(3-OH) residues possess the (Reconfiguration. The glycosylic phosphate group may be substituted by a phosphate group (see Table I) (46,65,69).

Fig. 3.—Chemical structure of the major component of Campylobacter jejuni lipid A. For details see the text. See also the legend to Fig. 2. For substituents of the phosphate groups see Table I. The a-anomeric phosphate has been tentatively assigned (97).

Fig. 6.—Chemical structure of the lipid A backbone of Neisseria meningitidis M986 LPS having polar substituents. The nonglycosylic and glycosylic phosphate groups are substituted by Etn-P to a similar degree (85 vs 80%, w/w). The anomeric configuration of the phosphate has been assigned tentatively as a. R1 = 12 0(3-OH), R2 = 14-O[12 0(3-OH)] (73).

Fig. 7.—Chemical structure of lipid A of Rhodobacter capsulatus. Dashed lines indicate nonstoichiometric substitution. The anomeric a configuration of phosphates and the configuration (Zor ) of the double bond in A5-12 1 are assigned only tentatively (89). For substituents of the phosphates see Table I. 

Fig. 8.—Chemical structure of lipid A of Rhodobacter sphaeroides (87,88,164). For details see the text and the legend to Fig. 6.

Fig. 11.—Chemical structure of the two preponderant lipid A forms of Pseudomonas aeruginosa. (A) Pentaacyl lipid A (major lipid A fraction 75%, w/w). (B) Hexaacyl lipid A (minor lipid A fraction, 25%, w/w). Dashed lines indicate nonstoichiometric a-hydroxylation of 12 0. A lipid A species having 2 mol 12 0(2-OH)/mol lipid A was not detected (77).

Single crystals of free lipid A or LPS are as yet not available. Therefore, the most promising approach to obtain molecular models is to perform theoretical calculations. After the chemical structures of enterobacterial lipid A had been elucidated, this methodology was successfully applied with heptaacyl S. minnesota lipid A (220) and hexaacyl E. coli Re LPS (221). As an example, Fig. 13 shows the atomic model of the E. coli lipid A molecule, as calculated by Kastowsky et al. (221) using energy-minimization techniques. 

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