Characterization of urinary degradation products derived from type I collagen. Identification of a beta-isomerized Asp-Gly sequence within the C-terminal telopeptide (alpha1) region.
The heterogeneity of urinary degradation products of C-terminal telopeptides derived from the alpha1 chain of human type I collagen was investigated and characterized. The urinary fragments characterized in this study consisted of two cross-linked (X) amino acid sequences derived from the C-terminal telopeptide (alpha1) of type I collagen. Fragments containing the sequence EXAHDGGR, with a DG site being either nonisomerized (Asp-Gly) or beta-isomerized (betaAsp-Gly), were identified. Pyridinoline was detected among the pyridinium cross-links, but there was a dominance of deoxypyridinoline and a cross-link containing pyridinoline having a molecular weight identical with that of galactosyl pyridinoline. A nonfluorescent cross-link was also found. The concentration of fragments derived from the C-terminal telopeptide region of type I collagen containing the sequence Asp-Gly (alphaCTX) and/or betaAsp-Gly (betaCTX) was measured by enzyme-linked immunosorbent assays in urine and in collagenase digests of trabecular and cortical bone of young and old origin. It was shown that the urinary ratio between such fragments, alphaCTX/betaCTX, was higher in children compared with adults and that the ratio decreased with increasing age of bone. The results indicated that the C-terminal telopeptide fragments derived from type I collagen excreted into urine originated mainly from bone. In conclusion, it is demonstrated for the first time that the C-terminal telopeptide alpha1 chain of type I collagen contains an Asp-Gly site prone to undergo beta-isomerization and that the degree of beta-isomerization of this linkage apparently increases with increasing age of bone. These findings indicate that the ratio alphaCTX/betaCTX might be clinically important in diagnosing metabolic bone diseases.
Fledelius
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Osteometer BioTech A/S, Herlev Hovedgade 207, DK-2730 Herlev, Denmark.
Johnsen
A H
AH
Cloos
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PA
Bonde
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Qvist
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D000328:Adult; D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal; D001224:Aspartic Acid; D001842:Bone and Bones / Q000737:chemistry; D002648:Child; D002851:Chromatography, High Pressure Liquid; D003094:Collagen / Q000032:analysis* / Q000652:urine*; D024042:Collagen Type I; D004797:Enzyme-Linked Immunosorbent Assay; D005998:Glycine; D006801:Humans; D007536:Isomerism; D008969:Molecular Sequence Data; D010455:Peptides / Q000032:analysis*
D000911:Antibodies, Monoclonal; D024042:Collagen Type I; D010455:Peptides; C052929:collagen type I trimeric cross-linked peptide; D001224:Aspartic Acid; D003094:Collagen; D005998:Glycine