The recently completed genome of the basidiomycete, Phanerochaete chrysosporium, revealed the presence of one NADPH-cytochrome P450 oxidoreductase (CPR: EC 1.6.2.4) gene and > 123 cytochrome P450 (CYP) genes, How single CPR can drive many CYPs is an important area Of study. We have investigated this CPR to gain insight into the mechanistic and structural biodiversity of the cytochrome P450 catalytic system. Native CPR and a NH2-terminally truncated derivative lacking 23 amino acids have been over-expressed in Escherichia coli and purified to electrophoretic homogeneity. Steady-state kinetics of cytochrome c reductase activity revealed a random Sequential bireactant kinetic mechanism in which both products form dead-end complexes reflecting differences in CPR kinetic mechanisms e en within a single kingdom of life. Removal of the N-terminal anchor of P. chrysosporium CPR did not alter the kinetic properties displayed by the enzyme in vitro, indicating it was a useful modification for structural studies. (C) 2002 Elsevier Science (USA). All rights reserved.