Hydroxyprolyl residues

Collagen triple helices are stabilized by hydrogen bonds between residues in dijferent polypeptide chains. The hydroxyl groups of hydroxyprolyl residues also participate in interchain hydrogen bonding. Additional stability is provided by covalent cross-links formed between modified lysyl residues both within and between polypeptide chains. 

This enzyme [EC 1.14.11.7], also known as procolla-gen proline, 2-oxoglutarate 3-dioxygenase, catalyzes the reaction of a prolyl residue in procoUagen with dioxygen and a-ketoglutarate (or, 2-oxoglutarate) to produce a irans-3-hydroxyprolyl residue in procollagen, succinate, and carbon dioxide. This reaction also requires iron ions and ascorbate. 

Prolyl residue a-Ketoglutarate 4-Hydroxyprolyl residue Succinate... 

It is important to be able to determine which chromatography column fractions contain polysaccharides and, specifically, which fractions contain hexosyl, pentosyl, or uronosyl residues. It is also important to detect in the fractions the presence of proteins and the presence of the specific amino acid characteristic of wall proteins, hydroxyproline. The detection of these substances is carried out by facile and sensitive colorimetric procedures. Although these reactions are not discussed here, the most frequently used colorimetric assays in our laboratory are the anthrone assay for detection of hexosyl residues 50), the orcinol assay for detecting pentosyl residues 50), the m-hydroxy-diphenyl assay for detection of uronosyl residues 35), the Lowry assay for detection of proteins 90), and the Kivirikko and Liesmaa assay for the detection of hydroxyprolyl residues 76). 

Next, we discuss the collagen, which takes the triple helix structure. The amino acid sequence of collagen fibril consists of the repeating amino-acid sequence unit [Gly-Xaa-Yaa]n, where Xaa and Yaa are frequently occupied by prolyl (Pro) and 4-hydroxyprolyl (Hyp) residues, respectively. It is well known that the sequential model polypeptides such as [Pro-Ala-Gly]n or [Pro-Pro-Gly]n take the triple-helix conformation similar to that of collagen, as studied by X-ray diffraction and C, N CP-MAS NMR. This section focuses on the structure of [Pro-Ala-Gly]n, and the collagen structure as described by H CRAMPS NMR. 

Conversions of peptide-prolyl and peptide-lysyl residues to hydroxyprolyl and hydroxylsyl residues are accomplished by iron-dependent enzymes utilizing... 

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