Crystallization, preliminary diffraction and electron paramagnetic resonance studies of a single crystal of cytochrome P450nor.

Cytochrome P450nor (P450nor) is a heme-containing nitric oxide reductase from the denitrifying fungus, Fusarium oxysporum. This enzyme catalyzes the reduction of NO to N2O. In the present study, we report results from preliminary crystallographic and electron paramagnetic resonance (EPR) analysis of a single crystal of P450nor. The crystal was grown in 100 mM MES buffer at pH 5.6 using PEG 4000 as a precipitant. It belongs to the orthorhombic system with cell dimensions of a = 54.99 A, b = 82.66 A, c = 87.21 A, and the space group is P2(1)2(1)2(1). The crystal diffracts synchrotron radiation at higher than 2.0 A resolution, and therefore it is suitable for X-ray crystal structure analysis at atomic resolution. Bijvoet and dispersive anomalous difference Patterson maps show a clear peak corresponding to the heme iron. The structure solution is currently underway by means of MIR and MAD techniques. EPR analysis determined the orientation of the heme within the P450nor crystal.