<prompt> All of the following are required for hydroxylation of proline residues except:Ascorbic acidGlutamateFerrous ionsMolecular oxygen  <response>: Ans. B. GlutamateProline is an imino acid. It undergoes hydroxylation to form collagen in the body. It is the principal residue in proteins to be hydroxylated. Hydroxylation is the process of attachment of hydroxyl group in the presence of large, multi-subunit enzymes prolyl 4-hydroxylase, prolyl 3-hydroxylase and lysyl 5-hydroxylase, respectively. These reactions require iron as well as molecular oxygen and a-ketoglutarate to carry out the oxidation, and use ascorbic acid vitamin C to return the iron to its oxidized state. Deprivation of ascorbate leads to deficiencies in proline hydroxylation, which leads to less stable collagen, which can manifest itself as the disease scurvy. 