Evidence for Basic Ferryls in Cytochromes P450
journal contributionposted on 06.09.2006, 00:00 by Rachel K. Behan, Lee M. Hoffart, Kari L. Stone, Carsten Krebs, Michael T. Green
Using a combination of Mössbauer spectroscopy and density functional calculations, we have determined that the ferryl forms of P450BM3 and P450cam are protonated at physiological pH. Density functional calculations were performed on large active-site models of these enzymes to determine the theoretical Mössbauer parameters for the ferryl and protonated ferryl (FeIVOH) species. These calculations revealed a significant enlargement of the quadrupole splitting parameter upon protonation of the ferryl unit. The calculated quadrupole splittings for the protonated and unprotonated ferryl forms of P450BM3 are ΔEQ = 2.17 mm/s and ΔEQ = 1.05 mm/s, respectively. For P450cam, they are ΔEQ = 1.84 mm/s and ΔEQ = 0.66 mm/s, respectively. The experimentally determined quadrupole splittings (P450BM3, ΔEQ = 2.16 mm/s; P450cam, ΔEQ = 2.06 mm/s) are in good agreement with the values calculated for the protonated forms of the enzymes. Our results suggest that basic ferryls are a natural consequence of thiolate-ligated hemes.