CRYSTAL STRUCTURE OF RAT LIVER NADPH-CYTOCHROME P-450 REDUCTASE. Ming Wang, David L. Roberts, Rosemary Paschke, Thomas Shea[[section]], Bettie Sue S. Masters[[section]] and Jung-Ja P. Kim , Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI 53226 and [[section]]Department of Biochemistry, University of Texas Health Science Center at San Antonio, San Antonio, TX 78284.

NADPH-cytochrome P-450 reductase (CPR) catalyzes the transfer of electrons from NADPH to all known microsomal cytochromes P450. CPR consists of a large 70 kDa cytoplasmic domain that contains both FMN and FAD as well as a NADPH binding domain, and a small, ~50 residue hydrophobic N-terminal domain responsible for anchoring the protein to the endoplasmic reticulum or nuclear envelope of most eukaryotic cells. Electron transfer proceeds from NADPH to FAD to FMN and finally to the heme of cytochrome P-450.

We have crystallized the cloned cytoplasmic domain of rat CPR and have collected a native data set to 2.6 on a Rigaku R-AXIS image plate detector with R_sym = 7.1%. The crystals belong to the orthorhombic space group P2₁2₁2₁ , with unit cell parameters a= 103.28, b= 116.18 and c= 119.77 %. The V_m is 2.6%³/dalton, with two molecules per asymmetric unit. The two molecules are related by a local two fold axis which is almost parallel to c.

The structure has been solved to 3.0 by MIR, with four heavy atom derivatives and a figure of merit was 0.595. The phases were extended and improved by using solvent flattening and local-two-fold averaging to 3 %. The model was built by using the TURBO package and refined by XPLOR. The current R factor is 27.8%. Further refinement is in progress.

This work was supported by NIH grant GM29076 (JJPK).