Phenol hydroxylase from Pseudomonas sp. CF600 is a member of a family of binuclear iron-center-containing multicomponent oxygenases, which catalyzes the conversion of phenol and some of its methyl-substituted derivatives to catechol. In addition to a reductase component which transfers electrons from NADH, optimal turnover of the hydroxylase requires P2, a protein containing 90 amino acids which is readily resolved from the other components. The three-dimensional solution structure of P2 has been solved by 3D heteronuclear NMR spectroscopy. On the basis of 1206 experimental constraints, including 1060 distance constraints obtained from NOEs, 70 phi dihedral angle constraints, 42 psi dihedral angle constraints, and 34 hydrogen bond constraints, a total of 12 converged structures were obtained. The atomic root mean square deviation for the 12 converged structure with respect to the mean coordinates is 2.48 A for the backbone atoms and 3.85 A for all the heavy atoms. This relatively large uncertainty can be ascribed to conformational flexibility and exchange. The molecular structure of P2 is composed of three helices, six antiparallel beta-strands, one beta-hairpin, and some less ordered regions. This is the first structure among the known multicomponent oxygenases. On the basis of the three-dimensional structure of P2, sequence comparisons with similar proteins from other multicomponent oxygenases suggested that all of these proteins may have a conserved structure in the core regions.