= Prolyl 4-hydroxylase
In <collagen> synthesis, <prolyl 4-hydroxylase> is the <enzyme> that converts selected peptide-bound <proline> residues into <Trans-4-hydroxy-L-proline>. The official name procollagen-proline 4-dioxygenase emphasizes both the protein substrate and oxygen-dependent reaction. It acts on <procollagen> and other <proteins> with collagen-like domains.<Prolyl 4-hydroxylase in IUBMB Enzyme Nomenclature>[EC 1.14.11.2, Reaction and Comments]{ref}
The reaction couples hydroxylation of a proline residue to conversion of <2-Oxoglutarate> into <succinate> and <carbon dioxide>, consuming molecular oxygen. The enzyme requires ferrous <iron> and <vitamin C>. It operates in the lumen of the <endoplasmic reticulum> and recognizes sequences containing $\mathrm{X\!\! -\!Pro\! -\!Gly}$, where $\mathrm X$ denotes a variable residue and Gly denotes <glycine>.<Prolyl 4-hydroxylase in IUBMB Enzyme Nomenclature>[Reaction, cofactors, location and sequence preference]{ref}
This is a <post-translational modification>: the peptide chain exists before its proline side groups are hydroxylated. The modified residues support the collagen triple helix. In a simplified fully coupled assay, one mole of hydroxylated residues corresponds to one mole of <succinate> formed. Measuring a coproduct can therefore report reaction progress, provided appropriate controls establish that it comes from the coupled enzyme reaction rather than other sources.
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