Hydroxyl amino acid

Hydroxylated amino acids (eg, 4-hydroxyproline, 5-hydroxylysine) and A/-methylated amino acids (eg, /V-methylhistidine) are obtained by the acid hydrolysis of proteins. y-Carboxyglutamic acid occurs as a component of some sections of protein molecules it decarboxylates spontaneously to L-glutamate at low pH. These examples are formed upon the nontranslational modification of protein and are often called secondary protein amino acids... 

These conditions were chosen specifically to facilitate the silylation of hydroxylated amino acids. 

Hydroxylated amino acids, 2 554 Hydroxylated PCBs, 13 143-144 biochemical effects of, 73 143-144 Hydroxylation, 9 278 12 183-184 Hydroxyl compounds... 

Parallel synthesis of 62 different fucosylated tripeptides resulted in two ligands with submicromolar affinity for the P-selectin however, the desired activity for the E-selectin was not observed.98 For the E-selectin selectivity, it was necessary to incorporate a hydroxyl group that mimics the 4-hydroxyl of the central Gal in SLex in addition to a Fuc-residue and a carboxylate to obtain ligands with > 10-fold increased activity over that of the SLex tetrasaccharide.81 One of the best ligands was obtained from Thr(a-Fuc)-OEt, which was first /V-acylated with a hydroxyl amino acid and then elongated with a di-acid to furnish the acid mimic of the sialic acid carboxylate (Fig. 14.4). This approach was further developed as a solid-phase method where the molecule was linked to a solid support through the invariable fucosyl moiety.99... 

The triplet Cly-X-Y is constantly repeated in the sequence of the triple-helical regions— i. e., every third amino acid in such sequences is aglycine. Proline (Pro) is frequently found in positions X or Y the Y position is often occupied by 4-hydroxyproline (4Hyp), although 3-hydroxyproline (3Hyp) and 5-hydroxylysine (5Hyl) also occur. These hydroxylated amino acids are characteristic components of collagen. They are only produced after protein biosynthesis by hydroxylation of the amino acids in the peptide chain (see p. 62). 

Cyclic peptides are important biologically active compounds that combine peptide properties with conformational bias and often improved serum stability and membrane penetration [1-3]. Depsipeptides are similar compounds, but they contain as part of their backbone one or more hydroxylated amino acid residues that add ester or lactone moieties to the peptide (Fig. 1) [4-6]. Cyclo- and... 

Despite the apparent advantages in the amide-containing amino acids, we do not always find amides used as part of the recognition sequence. For example, the trp repressor does not use any amides. The basic amino acids, lysine and arginine, and the hydroxylic amino acid, threonine, are the main interacting amino acids in the trp repressor. The side... 

The NCA 138 represents the amino-protected and carboxy-activated form of poly-oxamic acid 140, the hydroxylic amino acid portion of the antifungal family of polyoxins 139, Fig. 8. Other polyolic NCAs such as 141,142, and 143, Fig. 9, have also been prepared from the corresponding a-hydroxy p-lactams with equal success [123, 124]. 

The high content in hydroxyl amino acids (serine and threonine) may imply that hydroxyl-containing side chains are involved in silica deposition. Glycine, because of its small size may serve as a convenient spacer in the protein molecule. The notable reduction in the acidic residues between cytoplasmic protein and cell wall protein indicates that carboxyl groups are not the primary functional groups involved in Si-deposition. The following mineralization scheme is proposed548 ... 

One-third of the amino acid residues in collagen are Gly, while another quarter are Pro. The hydroxylated amino acids 4-hydroxyproline (Hyp) and 5-hydroxylysine (Hyl) are formed post-translationally by the action of proline hydroxylase and lysine hydroxylase. These Fe2+-containing enzymes require ascorbic acid (vitamin C) for activity. In the vitamin C deficiency disease scurvy, collagen does not form correctly due to the inability to hydroxylate Pro and Lys. Hyl residues are often post-translationally modified with carbohydrate. 

Composition and The amino acid composition of collagen is quite distinctive. Nearly one-third of post-translational its residues are Gly, while another one-quarter are Pro, significantly higher modifications proportions than are found in other proteins. The hydroxylated amino acids... 

Oxazoles are formed by decarboxylation of hydroxylated amino acids such as serine or threonine followed by condensation with aldehydes and cyclization. 

Analysis showed that the snail agglutinin contained a preponderance of acidic and hydroxylic amino acids and a large proportion of proline residues.83,560-562 Uncharacteristic of lectins from leguminous-plant seeds, the hemagglutinin contained 18 half-cystine residues and 10 molecular proportions of methionine per molecule of protein.83,569 About 8% (by weight) of covalently bound carbohydrate was found this was principally D-galactose and D-mannose.63... 

The properties of the isolated peptides were quite similar in nature, whereby each peptide consisted of 12 amino acids in length and possessed a munber of residues with functional side groups that could stabilize nanoclusters. In many instances, these side chains were the hydroxyl-terminated side chains of serine, threonine, and tyrosine. In two of the peptides (AG3 and AG4), the location of the hydroxylated amino acids was conserved within two of the peptides. Similarly, one proline amino acid was conserved throughout all three of the sequences. Upon incubating each peptide in a solution of silver nitrate with no exogenous reductant, a clearly observable plasmon resonance peak arose at 440 nm for AG3 and AG4, but not with AG5. The peak was quite broad, indicative of a disperse size and shape distribution. The main difference between the active peptides and inactive AG5 was an overall basic isoelectric point for AGS The assays were performed at neutral conditions which would modulate the side-chain dynamics under acidic or basic conditions. 

Other hydroxylated amino acids synthesized using 2-TST include 5-0-carbamoyl polyxamic acid <2000S1409> and the natural pseudopeptide antimicrobial agent AI-77-B <20010L2677, 2003EJ0821>. 

Recent studies on separation optimization showed that accurate control of mobile phase pH was essential to successfully resolve a number of important non-hydrolysate amino acids. With good control of a complex gradient profile the system could resolve a mixture of amino acids including, Asn, Gin, cysteine derivatives carboxymethyl cysteine and pyridylethyl cysteine, and the hydroxylated amino acids hydroxyproline (Hyp) and hydroxylysine (Hyl) as well as the hydrolysate amino acids (4). However, the required precision in the control of eluent pH unnecessarily complicated transfer of the method between laboratories. The method also lacked the ability to separate Orn from the hydrolysate amino acids. The current study demonstrates the utility of quaternary HPLC gradient systems for facilitating methods development and simplifying routine eluent preparation with excellent pH control. 

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