4-hy·drox·y·pro·line (4Hyp, Hyp),

4-hydroxy-2-pyrrolidinecarboxylic acid; the trans-l-isomer is a pyrrolidine found among the hydrolysis products of collagen; not found in proteins other than those of connective tissue. A vitamin C deficiency will result in impaired formation of hydroxyproline.
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Determination of 4-hydroxyproline was performed according to the procedure suggested by Kindt et al.
Collagen chains that do not contain 4-hydroxyproline cannot fold into triple helical molecules that are stable at body temperature (Pihlajaniemi et al.
13,14) Collagen contains 12% of the aminoacid proline and 9% of 4-hydroxyproline.
Collagen hydrolysate provides the specific amino acids -- glycine, proline and 4-hydroxyproline -- needed for joint cartilage synthesis.
Prolyl 4-hydroxylase catalyzes the hydroxylation of proline residues in repeating X-Pro-Gly triplets, thus forming the 4-hydroxyproline required for the correct folding of newly synthesized collagen (Kivirikko and Myllyharju, 1998; Kivirikko and Pihlajaniemi, 1998; Myllyharju, 2003).
Its primary sequence exhibits tandem repeats of the decapeptide motif Ala-Lys-Pro-Ser-Tyr-diHyp-Hyp-Thr-DOPA-Lys, where diHyp and Hyp are 3,4-dihydroxyproline and 4-hydroxyproline, respectively (Waite et al.