Hydroxyproline, 3-, collagen

The principal protein of skin and connective tissue is called collagen and is primarily constituted of glycine, proline, and hydroxyproline. Collagen is made up of tropocollagen, a substance with very long and thin molecules (14 X 2900 A, MW about 300,000). Each tropocollagen molecule consists of three twisted polypeptide strands. When collagen is boiled with water, the... 

Thus, the major abnormalities of plasma free hydroxyproline appear to result from (1) the ingestion of hydroxyproline, collagen, or gelatin in any form, and (2) an inability to metabolize hydroxyproline from either prematurity or an inborn error of metabolism. Theoretically, a... 

Figure 14.1 Each polypeptide chain in the collagen molecule folds into an extended polyproline type II helix with a rise per turn along the helix of 9.6 A comprising 3.3 residues. In the collagen molecule three such chains are supercoiled about a common axis to form a 3000-A-long rod-like molecule. The amino acid sequence contains repeats of -Gly-X-Y- where X is often proline and Y is often hydroxyproline. (a) Ball and stick model of two turns of one polypeptide chain.

The amino acids proline and hydroxyproline exert a stabilizing influence on the triple helix as described in detail in Sect. 4.5. By examining the CB peptides of collagen, a structural stability which is directly proportional to the itnino acid content may thus be found. It has, however, not been possible to synthesize model peptides displaying structural stability comparable to that of the native peptides having corresponding amino acid contents. 

Schoeninger, M.J. and DeNiro, M.J. 1984 Nitrogen and carbon isotopic composition of bone collagen from marine and terrestrial animals. Geochimica et Cosmochimica Acta 48 625-639. Schuette, S. A., Hegsted, M., Zemel, B. and Linkswiler, H.M. 1981 Renal acid, urinary cyclic AMP, and hydroxyproline excretion as affected by level of protein, sulfur amino acids and phosphorus intake. Journal of Nutrition 111 2106-2116. 

Fig. 4. Helical structure of collagen, typical amino acid sequence within a collagen strand, and exchangeable versus non-exchangeable hydrogen atoms in an individual leucine molecule (Gly - glycine. Pro - Proline, Leu - leucine. Hyp - hydroxyproline.

Very few post-translational modifications have been found on tropoelastin. However, hydroxylation of 25% of the proline residues is observed [10]. The enzymatic modification of proline to hydroxyproline (Hyp) is performed by prolyl hydroxylase [11]. The purpose of this hydroxylation remains unclear and it is even proposed that Hyps in tropoelastin are a by-product of collagen hydroxylation as this occurs in the same cellular compartment [8]. 

Results of amino acid analysis performed on resilin from the locust Schistorcerca gregaria, compared with values for collagen, elastin, and silk fibroin. Reproduced from [145] with permission from Elsevier, copyright Elsevier 1961 Includes 106 hydroxyproline and 7 hydroxylysine... 

Masaoka, T., F. Akahori, S. Arai, and K. Sakaguchi. 1987. Effect of paraquat on plasma fibronectin, serum free hydroxyproline, serum ceruloplasmin and lung collagen content in monkeys. J. Toxicol. Sci. 12 329-340. 

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