Pressure-Induced Rearrangement of Aryl-Iron Complexes in Cytochrome P-450cam: Application to Topological Mapping of the Compressed Active Site

Abstract

The reactions of cytochrome P-450cam with phenyldiazene result in the formation of phenyl-iron complexes. Oxidation of such complexes at 1 bar causes regioselective migration of the phenyl group from the iron to the porphyrin nitrogens. The four N-arylprotoporphyrin IX regioisomers formed indicate that the active site is open above pyrrole ring D and to a small extent above pyrrole ring C. The iron-aryl complexes decompose at pressures above 1500 bar for Fe-phenyl or 2500 bar for Fe-(2-naphthyl and Fe-(p-biphenyl) complexes. The kinetics of the decomposition processes exhibit negative activation volumes. Decompression of the solutions shows that the loss of the Fe-aryl complexes is associated with the formation of new distributions of the N-arylprotoporphyrin IX regioisomers. Thus the rearrangement of aryl-iron complexes can be induced by high pressure in the absence of any exogenous oxidizing agent. These results are interpreted in term of differential distortion of the P-450cam active site stucture induced by high pressure.