1,3-bis(2-pyridylimino)isoindoline, ind; 2OH-1,3-Ph2PD, 2-hydroxy-1,3-diphenylpropanedione; 6-Ph2TPA, N,N-bis[(6-phenyl-2-pyridyl)methyl]-N-[(2-pyridyl)-methyl]amine; ADO, cysteamine dioxygenase; AO, apocarotenoid 15,15'-oxygenase; ARD, aci-reductone dioxygenase; BsQDO, quercetin 2,3-dioxygenase from Bacillus subtilis; CD, circular dichroism; CDO, cysteine dioxygenase; CGDO, 5-chloro-gentisate 1,2-dioxygenase; CS2, clavaminate synthase; CarOs, carotenoid oxygenases; DFT, density functional theory; Dioxygen activation; Dioxygenase; Dke1, diketone dioxygenase; EPR, electron paramagnetic resonance; EXAFS, extended X-ray absorption fine structure spectroscopy; Enzyme catalysis; Facial triad; GDO, gentisate 1,2-dioxygenase; HADO, 3-hydroxyanthranilate 3,4-dioxygenase; HGDO, homogentisate 1,2-dioxygenase; HNDO, hydroxy-2-naphthoate dioxygenase; MCD, magnetic circular dichroism; MNHEs, mononuclear non-heme-Fe(II) dependent enzymes; Metal binding motif; NRP, nonribosomal peptide; OTf-, trifluormethanesulfonate; PDB, protein data bank; QDO, quercetin 2,3-dioxygenase; SDO, salicylate 1,2-dioxygenase; Structure­function relationships; TauD, taurine hydroxylase; XAS, X-ray absorption spectroscopy; acac, acetylacetone (2,4-pentanedione); fla, flavonolate; α-KG, α-ketoglutarate