An N-terminally modified form of the Arabidopsis NADPH-cytochrome P450 ATR2 (ATR2mod) was expressed from the tactac promoter in Escherichia colt to obtain high yields of the enzyme. The N-terminal modification eliminates the predicted chloroplast transit peptide of ATR2 allowing for more efficient expression. ATR2mod was purified from membrane extracts using a 2',5'-ADP-agarose affinity column. The specific activity of the purified ATR2mod for cytochrome c reduction was 9.4 mu mol min(-1) mg(-1) and the K-m for cytochrome c reduction was 15 +/- 2 mu M. The purified NADPH-cytochrome P450 reductase was able to support function of CYP79B2.