Cytochrome P450 enzymes catalyze a variety of reactions and are widely distributed in living organisms. In recent studies, the first members of five new families of cytochrome P450 enzymes have been identified, including cytochrome P450 219A1 (CYP219A1) from Novosphingobium aromaticivorans DSM 12444. It has also been reported that isolongifolen-9-one (C(15)H(22)O), a sesquiterpenoid ketone derivative, is a potential substrate for CYP219A1, inducing a >or=95% shift of the haem spin state to high spin upon binding. The CYP219A1 protein has been crystallized and single crystals have been studied by X-ray crystallography. Diffraction data were collected to 2.4 A resolution. The crystals belonged to space group P6, with unit-cell parameters a = 93.1, b = 93.1, c = 98.0 A. Preliminary X-ray diffraction data analysis revealed that the asymmetric unit contained one protein molecule.