modified amino acid metabolic process peptidyl-proline hydroxylation to 4-hydroxy-L-proline RESID:AA0030 biological_process GO:0018401 See also the molecular function term 'procollagen-proline 4-dioxygenase activity ; GO:0004656'. The modification of peptidyl-proline to form 4-hydroxy-L-proline; catalyzed by procollagen-proline,2-oxoglutarate-4-dioxygenase. peptidyl-proline hydroxylation L-amino acid metabolic process non-proteinogenic amino acid metabolic process