1 research outputs found
Setting an Upper Limit on the Myoglobin Iron(IV)Hydroxide p<i>K</i><sub>a</sub>: Insight into Axial Ligand Tuning in Heme Protein Catalysis
To provide insight into the iron(IV)hydroxide
p<i>K</i><sub>a</sub> of histidine ligated heme proteins,
we have probed the
active site of myoglobin compound II over the pH range of 3.9–9.5,
using EXAFS, Mössbauer, and resonance Raman spectroscopies.
We find no indication of ferryl protonation over this pH range, allowing
us to set an upper limit of 2.7 on the iron(IV)hydroxide p<i>K</i><sub>a</sub> in myoglobin. Together with the recent determination
of an iron(IV)hydroxide p<i>K</i><sub>a</sub> ∼ 12
in the thiolate-ligated heme enzyme cytochrome P450, this result provides
insight into Nature’s ability to tune catalytic function through
its choice of axial ligand