Spectroscopy and electrochemistry of cytochrome P450 BM3-surfactant film assemblies.
We report analyses of electrochemical and spectroscopic measurements on cytochrome P450 BM3 (BM3) in didodecyldimethylammonium bromide (DDAB) surfactant films. Electronic absorption spectra of BM3-DDAB films on silica slides reveal the characteristic low-spin FeIII heme absorption maximum at 418 nm. A prominent peak in the absorption spectrum of BM3 FeII-CO in a DDAB dispersion is at 448 nm; in spectra of aged samples, a shoulder at approximately 420 nm is present. Infrared absorption spectra of the BM3 FeII-CO complex in DDAB dispersions feature a time-dependent shift of the carbonyl stretching frequency from 1950 to 2080 cm(-1). Voltammetry of BM3-DDAB films on graphite electrodes gave the following results: FeIII/II E(1/2) at -260 mV (vs SCE), approximately 300 mV positive of the value measured in solution; DeltaS degrees (rc), DeltaS degrees , and DeltaH degrees values for water-ligated BM3 in DDAB are -98 J mol(-1) K(-1), -163 J mol(-1) K(-1), and -47 kJ mol(-1), respectively; values for the imidazole-ligated enzyme are -8 J mol(-1) K(-1), -73 J mol(-1) K(-1), and -21 kJ mol(-1). Taken together, the data suggest that BM3 adopts a compact conformation within DDAB that in turn strengthens hydrogen bonding interactions with the heme axial cysteine, producing a P420-like species with decreased electron density around the metal center.
Udit
Andrew K
AK
Department of Chemistry, Occidental College, Los Angeles, California 90041, USA. udit@oxy.edu
Hagen
Katharine D
KD
Goldman
Peter J
PJ
Star
Andrew
A
Gillan
James M
JM
Gray
Harry B
HB
Hill
Michael G
MG
D001426:Bacterial Proteins / Q000737:chemistry*; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry*; D004563:Electrochemistry / Q000379:methods*; D006899:Mixed Function Oxygenases / Q000737:chemistry*; D009251:NADPH-Ferrihemoprotein Reductase; D013057:Spectrum Analysis / Q000379:methods*; D013501:Surface-Active Agents / Q000737:chemistry*
D001426:Bacterial Proteins; D013501:Surface-Active Agents; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D009251:NADPH-Ferrihemoprotein Reductase; C052423:flavocytochrome P450 BM3 monoxygenases