TY - JOUR
T1 - Iron(IV)hydroxide pKa and the role of thiolate ligation in C-H bond activation by cytochrome P450
AU - Yosca, Timothy H.
AU - Rittle, Jonathan
AU - Krest, Courtney M.
AU - Onderko, Elizabeth L.
AU - Silakov, Alexey
AU - Calixto, Julio C.
AU - Behan, Rachel K.
AU - Green, Michael T.
PY - 2013
Y1 - 2013
N2 - Cytochrome P450 enzymes activate oxygen at heme iron centers to oxidize relatively inert substrate carbon-hydrogen bonds. Cysteine thiolate coordination to iron is posited to increase the pKa (where Ka is the acid dissociation constant) of compound II, an iron(IV)hydroxide complex, correspondingly lowering the one-electron reduction potential of compound I, the active catalytic intermediate, and decreasing the driving force for deleterious auto-oxidation of tyrosine and tryptophan residues in the enzyme's framework. Here, we report on the preparation of an iron(IV)hydroxide complex in a P450 enzyme (CYP158) in ≥90% yield. Using rapid mixing technologies in conjunction with Mössbauer, ultraviolet/visible, and x-ray absorption spectroscopies, we determine a pKa value for this compound of 11.9. Marcus theory analysis indicates that this elevated pKa results in a >10,000-fold reduction in the rate constant for oxidations of the protein framework, making these processes noncompetitive with substrate oxidation.
AB - Cytochrome P450 enzymes activate oxygen at heme iron centers to oxidize relatively inert substrate carbon-hydrogen bonds. Cysteine thiolate coordination to iron is posited to increase the pKa (where Ka is the acid dissociation constant) of compound II, an iron(IV)hydroxide complex, correspondingly lowering the one-electron reduction potential of compound I, the active catalytic intermediate, and decreasing the driving force for deleterious auto-oxidation of tyrosine and tryptophan residues in the enzyme's framework. Here, we report on the preparation of an iron(IV)hydroxide complex in a P450 enzyme (CYP158) in ≥90% yield. Using rapid mixing technologies in conjunction with Mössbauer, ultraviolet/visible, and x-ray absorption spectroscopies, we determine a pKa value for this compound of 11.9. Marcus theory analysis indicates that this elevated pKa results in a >10,000-fold reduction in the rate constant for oxidations of the protein framework, making these processes noncompetitive with substrate oxidation.
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U2 - 10.1126/science.1244373
DO - 10.1126/science.1244373
M3 - Article
C2 - 24233717
AN - SCOPUS:84887761225
SN - 0036-8075
VL - 342
SP - 825
EP - 829
JO - Science
JF - Science
IS - 6160
ER -