Hydroxyproline
Post-translationally hydroxylated proline residue characteristic of collagen; principal biochemical readout for tissue collagen content.
For laboratory and research use only — not for human consumption.
Hydroxyproline (Hyp, 4-hydroxyproline) is a non-standard amino acid produced by post-translational hydroxylation of proline residues in collagen and elastin by prolyl 4-hydroxylase, a mixed-function oxygenase requiring molecular oxygen, α-ketoglutarate, ferrous iron, and ascorbic acid (vitamin C) as cofactors. The hydroxyl groups on Hyp residues stabilise the collagen triple helix through inter-chain hydrogen bonding, giving collagen its characteristic tensile strength. Hyp comprises approximately 10-14% of collagen amino-acid content — the highest concentration of any protein in the mammalian body — making it a specific and quantitative biochemical marker of tissue collagen content. Vitamin C deficiency (scurvy) impairs Hyp synthesis, producing the connective-tissue fragility characteristic of the condition. Hyp is not reincorporated into new protein synthesis upon collagen turnover; it circulates and is excreted, providing an indirect marker of collagen degradation. In peptide research, tissue hydroxyproline assay (typically Neuman & Logan method or HPLC) is the standard biochemical readout for wound-healing collagen deposition, tendon collagen density, cardiac fibrosis assessment, and dermal regeneration studies. GHK-Cu-treated diabetic wounds show increased hydroxyproline content; BPC-157 tendon models correlate with hydroxyproline elevation; anti-fibrotic peptide models (AC-SDKP) show reduced pulmonary and cardiac hydroxyproline.