(2S,4R)-4-Hydroxyproline, or L-hydroxyproline (593), is a common , abbreviated as HYP, e.g., in .
Hydroxyproline is a major component of the . Hydroxyproline and proline play key roles for collagen stability. They permit the sharp twisting of the collagen helix. In the canonical collagen Xaa-Yaa-Gly triad (where Xaa and Yaa are any amino acid), a proline occupying the Yaa position is hydroxylated to give a Xaa-Hyp-Gly sequence. This modification of the proline residue increases the stability of the collagen triple helix. It was initially proposed that the stabilization was due to water molecules forming a hydrogen bonding network linking the prolyl hydroxyl groups and the main-chain carbonyl groups. It was subsequently shown that the increase in stability is primarily through and that hydration of the hydroxyproline residues provides little or no additional stability.
Hydroxyproline is found in few proteins other than collagen. The only other protein that includes hydroxyproline is . For this reason, hydroxyproline content has been used as an indicator to determine and/or amount.

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Solubility : Soluble in water
Appearance : White Crystalline Powder
Molecular Formula : C6H14N4O2
Purity : > 99%
Grade : Other, Pharmaceutical / Food Grade
Usage : Used in protein synthesis, supplementation, and clinical nutrition
Solubility : Freely soluble in water
Appearance : White crystalline powder
Molecular Formula : C5H11NO2S
Purity : 99% min
Grade : Other, Feed Grade, Food Grade, Pharma Grade
Usage : Animal feed, Pharmaceutical, Food Industry
Solubility : Slightly soluble in water, soluble in dilute acids and alkalis
Appearance : White crystalline powder
Molecular Formula : C13H14N2O3
Purity : 99% min
Grade : Other, Pharmaceutical Grade
Solubility : Soluble in water and dilute mineral acid and alkali hydroxide solutions
Appearance : White crystalline powder
Molecular Formula : C9H11NO2
Purity : 99%
Grade : Medicine Grade
Usage : Industrial