Protein ester links

Pig. 5.9 Mechanism proposed for formation of a covalent bond between a heme methyl and a protein carboxyl group. A similar sequence must occur again to form the second heme-protein ester link in the mammalian peroxidases. In the heme structure, V stands for -CH=CH2 and P for... 

The intracellular and plasma membranes have a complex structure. The main components of a membrane are lipids (or phospholipids) and different proteins. Lipids are fatlike substances representing the esters of one di- or trivalent alcohol and two aliphatic fatty acid molecules (with 14 to 24 carbon atoms). In phospholipids, phosphoric acid residues, -0-P0(0 )-O-, are located close to the ester links, -C0-0-. The lipid or phospholipid molecules have the form of a compact polar head (the ester and phosphate groups) and two parallel, long nonpolar tails (the hydrocarbon chains of the fatty acids). The polar head is hydrophihc and readily interacts with water the hydrocarbon tails to the... 

A similar pattern of reactivity has been observed by Burrows and coworkers for the reaction between A -acetyllysine methyl ester (Lys) and dG. This reaction was studied in order to gain an understanding of structural aspects of DNA-protein cross-links (DPCs). These cross-links are regarded as a common lesion of oxidative damage to cells, but remain, from a chemical point, a poorly understood DNA lesion. As pointed out by Burrows, oxidation of protein-DNA complexes should occur preferentially at the primary amines since these sites have a lower oxidation potential (1.1 V vs. NHE, pH 10) than G. While protonation of the primary amine inhibits the oxidative process, transient deprotonation of a lysine residue would give rise to a lysine aminyl radical (or aminium radical cation). Using... 

Photooxidation of the dGuo-5 -lysine ester leads to Z cross-linked to the lysine moiety (Morin and Cadet 1995), indicating that DNA-protein cross-links may also occur via such a process in case this amino acid happens to be in a proper position for the reaction to proceed. 

A subset of lactams is the P-lactam functionality, the chemistry of which has been studied extensively. The P-lactam functionality has been thoroughly studied because the biological activity of the P-lactam antibiotics (e.g., penicillins, cephalosporins, etc.) is the result of the presence of the P-lactam moiety (Fig. 9). The electrophilic carbonyl of the P-lactam reacts with certain penicillin binding proteins found in bacteria to form a covalent bond (ester-linked) with the protein (23,24). The protein is thereby inactivated, bacterial cell wall... 

Fig. 4. Scheme of NCL. The mechanism allows the straightforward preparation of small proteins with native backbone structures from fully unprotected synthetic peptide building blocks. The initial tran -thioesterification step includes the chemo-selective reaction between one peptide with a C-terminal a-thioester group (peptide 1) and second peptide with an N-terminal cysteine residue (peptide 2). Generated thio-ester-linked intermediate spontaneously rearranges to form a native peptide bond at the site of ligation. 

Fischer (1906) recognized the possibility of linkages between active side chains. Pauling and Niemann (1939) suggested that covalent cross-links such as disulfide bridges, side-chain ester links, and side-chain peptide links might be partly responsible for the configurational stability of proteins. 

The problem of mucopolysaccharide impurities will be discussed at the end of Section VI. This is of great importance to considerations of esterlike linkages as ester links may occur in certain mucopolysaccharides. They have been suggested as the chondroitin sulfate-protein links in a complex isolated from cartilage (Muir, 1958). 

A further relevance of glycoproteins to collagen is the nature of the protein-carbohydrate link found. Blumenfeld and Gallop (1962b) have shown that aspartic acid is involved in the ester-like links of collagen which may be binding hexose molecules. Aspartic acid also constitutes the point of attachment of carbohydrate in most glycoproteins studied to date. 

The cornified cell envelope is the outermost layer of a corneocyte, and mainly consists of tightly bundled keratin filaments aligned parallel to the main face of the corneocyte. The envelope consists of both protein and lipid components in that the lipid is attached covalently to the protein envelope. The envelope lies adjacent to the interior surface of the plasma membrane. " The corneocyte protein envelope appears to play an important role in the structural assembly of the intercellular lipid lamellae of the stratum corneum. The corneocyte possesses a chemically bound lipid envelope comprised of A-co-hydroxyceramides, which are ester linked to the numerous glutamate side chains provided possibly by both the ot-helical conformation and p-sheet conformation of involucrin in the envelope protein matrix. In the absence of A-oo-hydro-xyceramides, the stratum corneum intercellular lipid lamellae were abnormal and permeability barrier function was disrupted. 

The objective of this work was to study the demethylation of WEAX ester-linked ferulic acid in order to produce caffeic acid ester-linked onto WEAX, possibly oxidable into quinone and able to link an amino acid of a protein in a second step. To our knowledge, if free ferulic acid can be O-demethylated intact by some microorganisms,10 16 no microbial O-demethylation of linked methoxylated compounds has been reported in the literature. Three anaerobic bacteria (Acetobacterium woodi, Clostridium methoxybenzovorans and Eubac-terium callanderi) and one facultative aerobic bacterium (Enterobacter cloacae) have been chosen in different phylogenetic groups for their ability to O-demethylate free ferulic acid.10-13... 

Demethylation of Free and Ester-linked Ferulic Acid by Sonicated Cellular Extracts of SR3. The O-demethylase activity of the SR3 strain was not excreted in the culture medium. To demethylate ferulic acid esterified to WEAX, which cannot penetrate the cells, a cell extract of SR3 strain was prepared by anaerobic sonication (MSON 05 Bio block, 20 Hz, 3 cycles of sonication of 2 min 2 s pulses separated by 2 s lag phase). The sonicated cellular extract of SR3 was tested in anaerobiose on free ferulic acid and esterified ferulic acid at 37 °C with a bacteria protein/ferulic acid ratio of 100 mg/ mol. Composition of reaction medium has been chosen in agreement with previous works on the demethylation of methoxylated phenolic compounds by other strains.15 20-22 In order to limit the viscosity of the medium, a 0.5% arabinoxylan concentration was used, corresponding to a 50 / M ferulic acid concentration. 

Fig. 1. Structures of lipids covalently attached to proteins. Panel A shows proteins that are lipidated on cytoplasmi-cally exposed amino acids, whereas panel B shows lipidated proteins in the extracellular leaflet. (A) iV-myristoyl glycine, palmitate thioester-linked to cysteine, farnesyl, or geranylgeranyl (prenyl) thioether-linked to cysteine. (B) A/-palmitoyl cysteine, cholesterol ester-linked to glycine, and a minimal GPI anchor linked to the to amino acid in a GPI-anchored protein. The GPI structure is shown with a diacylglycerol moiety containing two ester-linked fatty acids. Other GPI anchors are based on ceramide, while yet others have monoacylglycerol, a fatty acid ether-linked to glycerol, and/or a fatty acid ester-linked to inositol.

Proof that the ester-linked fatty adds were predominantly (possibly even exclusively) confined to the cuticle was provided by studies of covalently bound fatty adds from isolated cuticle cells [61,62] and by TEM [63]. The culmination of the chemical research was the presentation of a model for the cuticle cell envelope, which proposed that the cuticle-air interface consisted of long-chain fatty acids covalently linked as thioesters to a heavily cross-linked protein membrane, forming a hydrophobic barrier at the surface of each cuticle cell [42] (Figure 5.6). 

Nucleotides bear the same relation to a nucleic acid that amino acids do to a protein they are its monomeric units. The connecting links in proteins are amide groups in nucleic acids they are phosphate ester linkages. Phosphate esters link the 3 -OH of one ribose (or deoxyribose) with the 5 -OH of another. This makes the nucleic acid a long unbranched chain with a backbone of sugar and phosphate units with heterocyclic bases protruding... 

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