The critical iron-oxygen intermediate in human aromatase.
Aromatase (CYP19) is the target of several therapeutics used for breast cancer treatment and catalyzes the three-step conversion of androgens to estrogens, with an unusual C-C cleavage reaction in the third step. To better understand the CYP19 reaction, the oxy-ferrous complex of CYP19 with androstenedione substrate was cryotrapped, characterized by UV-vis spectroscopy, and cryoreduced to generate the next reaction cycle intermediate. EPR analysis revealed that the initial intermediate observed following cryoreduction is the unprotonated g(1)=2.254 peroxo-ferric intermediate, which is stable up to 180K. Upon gradual cryoannealing, the low-spin (g(1)=2.39) product complex is formed, with no evidence for accumulation of the g(1)=2.30 hydroperoxo-ferric intermediate. The relative stabilization of the peroxo-ferric heme and the lack of observed hydroperoxo-ferric heme distinguish CYP19 from other P450s, suggesting that the proton delivery pathway is more hindered in CYP19 than in most other P450s.
Gantt
Stephanie L
SL
Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
Denisov
Ilia G
IG
Grinkova
Yelena V
YV
Sligar
Stephen G
SG
D001141:Aromatase / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D006801:Humans; D006861:Hydrogen Peroxide / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*
D006861:Hydrogen Peroxide; D007501:Iron; D001141:Aromatase; D010100:Oxygen