Electrochemistry and Bioelectrocatalysis of Cyt P450 3A4 Baculosomes in LbL Films in a CTAB Microemulsion

This paper describes electrochemical studies of stable, cyt P450 3A4 baculosome films formed layer-by-layer (LbL) with polyions on pyrolytic graphite electrodes at 25 and 37 °C in a cetyltrimethylammonium (CTAB) bicontinuous microemulsion. The baculosomes also contain cyt P450 reductase (CPR) and cyt b5. Reversible cyclic voltammograms (CVs) were obtained up to about 20 V/s scan rates, with kinetically-limited CVs set in at 20–50 V/s. Electron transfer rate constants (ks) obtained from CV were 506 s–1 at 25 °C and 571 s–1 at 37 °C, 12.7 times larger than those for cyt P450s 1A2 and 2EI combined with CPR microsomes and cyt b5 in LbL films that had ks values at 25 °C close to 40 s–1. The peak potentials of the baculosome films that are much more negative than those of cyt P450s and cyt b5 suggest that electrons are first delivered from the electrode to CPR in the baculosomes, as also suggested earlier for films of CPR microsomes and cyt b5 containing cyt P450s 1A2 and 2EI and for multiple cyt P450s in human liver microsomes. Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) demonstrated the biocatalysis of O2 reduction and oxidation of thiochroman-4-one in O2-saturated CTAB microemulsions by the cyt P450 3A4 baculosome films. Controlled potential electrolysis using cyt P450 3A4 baculosome films oxidized thiochroman-4-one to give 48% yield of thiochroman-4-one 1-oxide with 70% enantiomeric excess (%ee) for the S enantiomer at 25 °C and 69% yield of thiochroman-4-one 1-oxide with 80%ee for the S enantiomer at 37 °C.