Hydroxy lysine

The other chiral component, the lactam 323, is clearly a cyclised version of 5-hydroxy-lysine 330. This and hydroxyproline 331 occur in the connective protein collagen. The hydroxy groups are added after the collagen is assembled but as they can be obtained by hydrolysis of collagen, they are members of the chiral pool. 

UDPgalactose-collagen galactosyltransferase UDPgalactose 5-hydroxy-lysine-collagen galactosyltransferase (EC 2.4.1.50) 155... 

There is some doubt about this enzyme since galactose is stated to be the only monosaccharide found to be attached directly to 5-hydroxy lysine in collagen (160). 

Hydroxy lysine, dehy d rolysino-norleucine. desmosine, pipecolic acid, mimosine. piperidine and quinolizidine alkaloids... 

Collagen constitutes 20-25% of the total protein in mammals. Table 12.6 shows data on its amino acid composition. The high contents of glycine and proline and the occurrence of 4-hydro-xyproline and 5-hydroxy lysine are characteristic. Since the occurrence of hydroxyproline is confined to connective tissue, its determination may provide quantitative data on the extent of connective tissue incorporation into a meat product. 

Some proteins may contain derivatives of common amino acids, e.g. collagen contains 5-hydroxy-lysine (Figure 1.6). Some amino acids which do not occur in proteins may function in cellular metabolism, e.g. citrulline and ornithine (Section 16.5). D-Amino acids occur alongside L-amino acids in some peptide antibiotics, e.g. valinomycin and actinomycin D, and in the peptidoglycan of the bacterial cell wall (Figure 3.10b). 

Hi. Lysine. Gamma radiolysis of aerated aqueous solution of lysine (94) has been shown, as inferred from iodometric measurements, to give rise to hydroperoxides in a similar yield to that observed for valine and leucine. However, attempts to isolate by HPLC the peroxidic derivatives using the post-column derivatization chemiluminescence detection approach were unsuccessful. This was assumed to be due to the instability of the lysine hydroperoxides under the conditions of HPLC analysis. Indirect evidence for the OH-mediated formation of hydroperoxides was provided by the isolation of four hydroxylated derivatives of lysine as 9-fluoromethyl chloroformate (FMOC) derivatives . Interestingly, NaBILj reduction of the irradiated lysine solutions before FMOC derivatization is accompanied by a notable increase in the yields of hydroxylysine isomers. Among the latter oxidized compounds, 3-hydroxy lysine was characterized by extensive H NMR and ESI-MS measurements whereas one diastereomer of 4-hydroxylysine and the two isomeric forms of 5-hydroxylysine were identified by comparison of their HPLC features as FMOC derivatives with those of authentic samples prepared by chemical synthesis. A reasonable mechanism for the formation of the four different hydroxylysines and, therefore, of related hydroperoxides 98-100, involves initial OH-mediated hydrogen abstraction followed by O2 addition to the carbon-centered radicals 95-97 thus formed and subsequent reduction of the resulting peroxyl radicals (equation 55). 

A quite different situation holds for collagen in which P-galactosyl units and glucosyl-P-galactosyl disaccharide units are attached to side chains of hydroxy-lysine formed by postsynthetic modification of the original procollagen chain. 

The overwhelming majority of foods contain amino acids, either in the free form (e.g., fruit juice) or in the form of protein (partially hydrolyzed or intact). Proteins are polymers, and their monomeric units are amino acids. Predominantly, proteins are comprised of 20 amino acids (see Fig. 1). In addition, some structural proteins contain large amounts of hydroxyproline (e.g., collagen). Far less abundant is the amino acid hydroxy lysine. The principal sources of dietary amino acids for humans are proteins, which are enzymatically digested to liberate their constituent amino acids. 

Collagen contains alcoholic groups in the hydroxyproline, serine, threonine, and hydroxy lysine moieties. Free radicals are probably formed at such sites which, in the presence of a vinyl monomer, serve to initiate grafted side chains. Since the free radicals are formed on the side chains of the substrate, a high grafting efficiency and a minimum amount of homopolymer formation compared with other redox systems can be expected. 

Collagen A protein, the main constituent of connective tissues and the organic component of bones It contains high concentrations of glycine (33%) and proline (13%) it also contains hydroxyproline (10%) and the uncommon hydroxy lysine (10%)... 

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