Cystine lipids

The nails are composed of flattened, keratinized cells, fused into a dense and hard, yet slightly elastic plate. Their thickness varies from 0.5 to 1.0 mm. In contrast to the stratum corneum (10%), the total lipid content of the nails lies between 0.1% and 1%, and the keratin domain is harder, due to higher sulfur content (cystine). Moreover, the water content is only 7% to 12%, in comparison to 25% in the stratum corneum. The relative water gain may not exceed 25% at 100% relative humidity, in sharp contrast to 200-300% as found in the stratum corneum. 

The oxidation of cysteine, as well as other amino acids, was studied by Mudd et a/. Individual amino acids in aqueous solution were exposed to ozone the reported order of susceptibility was cysteine, methionine, tryptophan, tyrosine, histidine, cystine, and phenylalanine. Other amino acids were not affected. This order is similar to that for the relative susceptibility of amino acrids to radiation and to lipid peroxides. Evaluation of the ozonization products revealed that cysteine was converted to cysteic acid, as well as cystine methionine to methionine sulfoxide tryptophan to a variety of pioducrts, including kynurenine and N-formylkynurenine tyrosine also to a variety of products, includiitg dihydroxyphenylalanine histidine to ammonia, proline, and other compounds and cystine in part to cysteic acid. In some cases, the rate and end products depended on the pH of the solution. 

Peroxynitrite (ONOO ) is a cytoxic species that is considered to form nitric oxide (NO) and superoxide (Oj ) in biological systems (Beckman et al. 1990). The toxicity of this compound is attributed to its ability to oxidize, nitrate, and hydroxylate biomolecules. Tyrosine is nitrated to form 3-nitrotyrosine (Ramazanian et al. 1996). Phenylalanine is hydroxylated to yield o-, m-, and p-tyrosines. Cysteine is oxidized to give cystine (Radi et al. 1991a). Glutathione is converted to S-nitro- or S-nitroso derivatives (Balazy et al. 1998). Catecholamines are oxidatively polymerized to melanin (Daveu et al. 1997). Lipids are also oxidized (Radi 1991b) and DNA can be scissored by peroxynitrite (Szabo and Ohshima 1997). 

In addition to enzymatic hydrolysis of natural lipids in polymeric membranes as discussed in chapter 4.2.2., other methods have been applied to trigger the release of vesicle-entrapped compounds as depicted in Fig. 37. Based on the investigations of phase-separated and only partially polymerized mixed liposomes 101, methods to uncork polymeric vesicles have been developed. One specific approach makes use of cleavable lipids such as the cystine derivative (63). From this fluorocarbon lipid mixed liposomes with the polymerizable dienoic acid-containing sulfolipid (58) were prepared in a molar ratio of 1 9 101115>. After polymerization of the matrix forming sulfolipids, stable spherically shaped vesicles are obtained as demonstrated in Fig. 54 by scanning electron microscopy 114>. 

In addition to cytochrome P-450 induction, other diet induced metabolic effects are likely to be involved in carcinogenesis. High temperature processing or long-term storage of foods with attendant exposure to oxygen can lead to the formation of lipid peroxides and oxidized sulfur amino acids in the food. The partially oxidized S-amino acids cystine monoxide (CMO) and methionine sulfoxide (MSO) are nutritionally available, but require in vivo conversion to the reduced amino acids at the... 

Chemically, human hair contains approximately 85 percent protein, 7 percent water, 3 percent lipid, 4.7 percent protein-bound sulfur (as cystine), and low concentrations of trace minerals (e.g., iron, zinc, copper). The phosphorus content is approximately 80 milligrams per 100 grams (0.003 ounces per 3.5 ounces) of hair. Hair is normally associated with sebum and exocrine secretions from skin glands that confer greasiness but influence its water content and mechanical and physical properties. 

L25. Lux, S. E., John, K. M., Fleischer, S., Jackson, R. L., and Gotto, A. M., Jr., Identification of the lipid-binding cyanogen bromide fiagment from the cystine-containing high density apolipoprotein, APOLP-GLN-II. Biochem. Biophys. Res. Common. 49, 23-29 (1972). 

The molar ratios of most of the amino acids in the protein of the German cockroach are generally similar to those of vertebrates and other invertebrates with respect to whole animal protein hydrolyzates (1). However, histidine, lysine, tyrosine, leucine, isoleucine, valine, and alanine are somewhat more abundant in cockroach protein and there is less cystine. The data vary significantly from data previously reported on the amino acid composition of the German cockroach (7). The earlier analysis, however, was conducted on insects with the entire head and digestive tract removed and the remaining portions of the body extracted with lipide solvents only. 

This reaction is catalyzed by manganese ions at pH values from 6 to 7.5. S02 can also react with cystine to yield a series of oxidation products. Some of the possible reaction products resulting from the oxidation of sulfur amino acids are listed in Table 3-11. Nielsen et al. (1985) studied the reactions between protein-bound amino acids and oxidizing lipids. Significant losses occurred of the amino acids lysine, tryptophan, and histidine. Methionine was extensively oxidized to its sulfoxide. Increasing water activity increased losses of lysine and tryptophan but had no effect on methionine oxidation. 

Hydrolysis with peracetic acid reveals a membrane composition of about 2/3 protein and 1/3 lipid, plus small amounts of carbohydrates (32). This protein incorporates nearly 13% proline, an amino acid that prevents normal helix formation (68, 75). Membranes also contain about 7 % of half-cystine units this composition may permit substantial disulfide bonding (68). The formation of cross linkages like those in insect cuticle is postulated (32). A common origin of membrane and KH proteins is suggested by their similarly high contents of proline and half-cystine residues (75). 

Animal experiments have shown that faulty nutrition, i.e. > 90% fat, < 10% protein and < 2 mg choline per day, leads to pronounced fatty fiver and even fatty cirrhosis within a few weeks. The same changes could be observed when the protein intake remained more or less normal, while extremely little methionine and choline was offered. With a partial surplus of certain foodstuffs, the special nature of the excessive nutritional components is also of considerable importance. The term partial malnutrition may, for example, be associated with a pronounced protein deficiency (and thus possibly inadequate production of lipoproteins) or a lack of lipotropic substances (such as methionine, choline, cystine, glycocoUbetaine, pyridoxine, casein and various N- or S-methylated substances). Protein deficiency has particularly severe consequences when toxic substances are absorbed at the same time or when the organism has to fight bacterial or parasitic infections. A diseased liver reacts to both a serious deficiency in and an excessive supply of different nutrients (e.g. proteins, certain kinds of amino acids, various lipids, trace elements) with unfavourable or even complicative developments during the course of disease. 

A protein can consist of two or more separate polypeptide chains linked together. Other, non-amino acid components such as minerals, lipids and carbohydrates can also be part of a protein. The quaternary structure describes how these different chains and components interact and connect to each other by hydrogen bonding, electrostatic attraction and sulfide bridges. Such sulfide bridges are formed by oxidation of the -SH groups of Cysteine (Fig. 1.18). The product of this reaction is a covalently bonded dipeptide called Cystin. 

Wool and hair have the most complex structures of any textile fibres. In the paper by Viney, fig. 1 shows how keratin proteins, of which there are more than one type, all having a complicated sequence of amino acids, assemble into intermediate filaments (IFs or microfibrils). But, as shown in Fig. 5a, this is only one part of the story. The microfibrils are embedded in a matrix, as shown in Fig. 5b. The keratin-associated proteins of the matrix contain substantial amounts of cy.stine, which cross-links molecules by -CH2-S-S-CH2- groups. Furthermore, terminal domains (tails) of the IFs, which also contain cystine, project into the matrix and join the cross-linked network. At a coarser scale, as indicated in Fig. 5c, wool is composed of cells, which are bonded together by the cell membrane complex (CMC), which is rich in lipids. As a whole, wool has a multi-component form, which consists of para-cortex, ortho-cortex, meso-cortex (not shown in Fig. 5a), and a multi-layer cuticle. In the para-and meso-cortex the fibril-matrix is a parallel assembly and the macrofibrils, if they are present, run into one another, but in the ortho-cortex the fibrils are assembled as helically twisted macrofibrils, which are clearly apparent in cross-section.s. 

Lipid oxidation products can interact with proteins and amino acids, and can affect the flavor deterioration and nutritive value of food proteins. Peroxyl radicals are very reactive with labile amino acids (tryptophane, histidine, cysteine, cystine, methionine, lysine and tyrosine), undergoing decarboxylation, decarbonylation and deamination. Methionine is oxidized to a sulfoxide combined cysteine is converted to cystine to form combined thiosulfinate (Figure 11.4). Aldehydes, dialdehydes and epoxides derived from the decomposition of hydroperoxides react with amines to produce imino Schiff bases (R-CH=N-R ). Schiff bases polymerize by aldol condensation producing dimers... 

The most important part of the cuticle from the point of view of polymer deposition is, of course, its outermost surface, i.e., the epicuticle. The epicuticle has been defined by Lindberg (11) as the membrane that contains sacs or bubbles raised upon immersion of wool fibers in chlorine water, i.e., the so-called Allwoerden reaction. It has been shown, however, that the removal of strongly bound surface lipids does not affect this phenomenon (12). It is assumed therefore, that the epicuticle, which is about 25 A thick, is a residue of the cuticle cell membrane and is at least partly proteinaceous in nature and, together with surface-bound lipids (9), forms the F-layer. A recent model of the epicuticle membrane proposed by Negri and co-workers (13) incorporates new evidence and defines the epicuticle in terms of a membrane consisting of 25% lipids and 75% protein, the latter having an ordered, possibly P-pleated sheet structure with 12% cystine, as shown in Figure 4. 

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