Hydroxylysine
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| Surname | Hydroxylysine | ||||||||||||||||||
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| Molecular formula | C 6 H 14 N 2 O 3 | ||||||||||||||||||
| Brief description |
beige powder (hydrochloride) |
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| Molar mass | 162.187 g mol −1 | ||||||||||||||||||
| Physical state |
firmly |
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| Melting point |
225–230 ° C (hydrochloride) |
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| As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . | |||||||||||||||||||
Hydroxylysine (more precisely 5-hydroxy- L- lysine , abbr. Hyl ) is a proteinogenic but non-canonical amino acid that was discovered in 1921 by Donald Van Slyke .
biosynthesis
Although found in proteins, this amino acid can not be incorporated directly into polypeptides during translation . Only after the incorporation of lysine can it be oxidized to hydroxylysine by the enzyme lysyl hydroxylase ( post-translational modification ).
Occurrence
5-Hydroxylysine is found in collagen (animals and humans only) and in some other glycoproteins such as adiponectin .
Hydroxylysine has also been found in bacteria, such as Staphylococcus aureus .
Within a collagen polypeptide, the distribution pattern of the hydroxylated lysines is neither rigid nor completely flexible; H. In certain positions, hydroxylation is never found, in some always (except for certain connective tissue diseases) and in others very often to very rarely. Within the collagen triple helix, hydroxylated lysine occurs almost only in the Y position of the Gly-XY sequence, i.e.: Gly-X-Hyl (for a more detailed explanation of the triple helix sequence, see collagen ). Within the short, non-triple-helical areas of collagen, it can also be found in other places (e.g. X-Hyl-Ala or X-Hyl-Ser).
properties
Like lysine, hydroxylysine has a free amino group in the side chain. It belongs to the group of basic amino acids or hexon bases, alongside arginine and histidine. These have a basic group that makes them react alkaline. The charge of the hydroxylysine is pH-dependent ( pK value : ≈10).
Functions
In some glycosylations, 5-hydroxylysine serves as a starting point for the first sugar residue. In collagen, it also fulfills this function on the one hand, and in other places it serves as a starting point for covalent cross-links between individual collagen molecules and between entire collagen fibrils .
A deficiency of hydroxylysine within the collagen molecules causes connective tissue weakness and is usually due to inactive lysyl hydroxylase. The reason for this can be a genetic abnormality ( Ehlers-Danlos syndrome VI) or poisoning (for example through the specific inhibitor BAPN = β-aminopropionitrile, accompanying poisoning in lathyrism ). A complete hydroxylysine deficiency is lethal, and in mammals it is unlikely that even a live birth is possible.
A deficiency of hydroxylysine within proteins cannot be compensated directly by the uptake of hydroxylysine, since at least a direct incorporation into polypeptides during translation is physiologically impossible. However, hydroxylysine is offered as a valuable dietary supplement . However, any particular benefit is questionable.
The prevention of the oxidation of lysine to hydroxylysine by the inhibitor BAPN for therapeutic purposes is considered.
determination
The hydroxylysine test in urine is used to quantify the collagen metabolism of the bones.
Individual evidence
- ↑ a b c d data sheet DL-5-Hydroxylysine hydrochloride from Sigma-Aldrich , accessed on October 20, 2016 ( PDF ).
- ^ W. Grady Smith, Daniel P. Gilboe, and LM Henderson: Incorporation of Hydroxylysine into the Cell Wall and a Cell-Wall Precursor in Staphylococcus aureus , in: J. Bacteriol. 1965, 1, 89, pp. 136-140; PMC 315560 (free full text).
- ↑ Patent US4444787 : Ophthalmic topical use of collagen cross-linking inhibitors. Published April 24, 1984 , inventor: Louise C. Moorhead.
- ↑ K. Yoshihara et al .: Urinary excretion levels of hydroxylysine glycosides in osteoporotic patients , In: Biol Pharm Bull . 1994, 6, 17, pp. 836-839; PMID 7951149 .