PRESSURE-INDUCED DEFORMATION OF THE CYTOCHROME P450(CAM) ACTIVE-SITE

The reaction of cytochrome P450(cam) with aryldiazenes (ArN=NH) yields sigma-bonded iron-aryl (Fe-aryl) complexes. Oxidation of the complexe s causes regioselective migration of the aryl group from the iron to t he porphyrin nitrogens. The influence of high pressure on the formatio n and rearrangement of the Fe-aryl complexes is reported here. The nat ural logarithm of the rate of formation of the Fe-phenyl complex decre ases linearly with pressure with a volume of activation of 38.2 mL mol (-1). The Fe-phenyl, Fe-(2-naphthyl), and Fe-(p-biphenyl) complexes ar e stable at atmospheric pressure but decompose in a pressure-dependent manner at pressures above 1500 (Fe-phenyl) or 2500 bar (Fe-(2-naphthy l) or Fe-(p-biphenyl)). This pressure-induced decomposition results in formation of the N-arylprotoporphyrin IX adducts. The N-aryl porphyri n regioisomer patterns obtained by pressure-induced migration of the a ryl groups (N-B:N-A:N-C:N-D, Ph, 10:14:33:43; 2-naphthyl, 12:13:37:38; p-biphenyl, 15:15:33:37) differ from those obtained by oxidation of t he P450(cam) Fe-aryl complexes at atmospheric pressure (Ph, 00:05:25:7 0; 2-naphthyl, 00:00:100:00; p-biphenyl, 00:14:40:46). Preincubation o f P450(cam) at elevated pressure followed by decompression, Fe-phenyl complex formation, and oxidative shift yields the same N-phenyl regioi somer ratio as the pressure-induced shift. The three principal finding s of this study are that (a) the iron-to-nitrogen migration of the ary l group can be promoted by pressure, (b) differential distortion of th e P450(cam) active site by high pressure causes small displacements of the I-helix and residues associated with the substrate access channel , and (c) pressure causes a subtle structural change in the P450(cam) active site that persists at atmospheric pressure.