TY - JOUR
T1 - Phosphate ester cleavage promoted by a tetrameric iron(III) complex
AU - Kantacha, Anob
AU - Buchholz, Rebecca
AU - Smith, Sarah J.
AU - Schenk, Gerhard
AU - Gahan, Lawrence R.
PY - 2011/1
Y1 - 2011/1
N2 - The purple acid phosphatases (PAPs) are the only binuclear metallohydrolases where the necessity for a heterovalent active site [Fe(III)-M(II) (M is Fe, Zn or Mn)] for catalysis has been established. The paradigm for the construction of PAP biomimetics, both structural and functional, is that the ligands possess characteristics which mimic those of the donor sites of the metalloenzyme and permit discrimination between trivalent and divalent metal ions. The donor atom set of the ligand 2-((2-hydroxy-5- methyl-3-((pyridin-2-ylmethylamino)methyl)benzyl)(2-hydroxybenzyl)amino)acetic acid (H3HPBA) mimics that of the active site of PAP although the iron(III) complex of this ligand has been characterized as the tetramer [Fe 4(HPBA)2(μ-CH3COO)2(μ-O)(μ- OH)(OH2)2]ClO4•5H2O. The phosphoesterase-like activity of the complex in 1:1 acetonitrile/water has now been investigated using the substrate 2,4-bis(dinitrophenyl)phosphate. The pH dependence of the catalytic rate revealed a non-symmetric bell-shaped profile, with a finite but non-zero rate at high pH. Unlike the traditional approach usually employed to analyse these bell-shaped profiles, the approach used here involved incorporating additional species which contribute to the overall activity. Employing this approach, we show that the complex has a k cat of 1.6 (±0.2) × 10-3 s-1, three kinetically relevant pK a values of 5.3, 6.2 and 8.4, with K M of 7.4 ± 0.6 mM. The kinetic parameters are similar to those reported for heterovalent PAP biomimetics. Additionally, it is observed that, unlike the enzyme, the oxidation state is not the determining factor for catalytic activity. Graphical Abstract: [Figure not available: see fulltext.]
AB - The purple acid phosphatases (PAPs) are the only binuclear metallohydrolases where the necessity for a heterovalent active site [Fe(III)-M(II) (M is Fe, Zn or Mn)] for catalysis has been established. The paradigm for the construction of PAP biomimetics, both structural and functional, is that the ligands possess characteristics which mimic those of the donor sites of the metalloenzyme and permit discrimination between trivalent and divalent metal ions. The donor atom set of the ligand 2-((2-hydroxy-5- methyl-3-((pyridin-2-ylmethylamino)methyl)benzyl)(2-hydroxybenzyl)amino)acetic acid (H3HPBA) mimics that of the active site of PAP although the iron(III) complex of this ligand has been characterized as the tetramer [Fe 4(HPBA)2(μ-CH3COO)2(μ-O)(μ- OH)(OH2)2]ClO4•5H2O. The phosphoesterase-like activity of the complex in 1:1 acetonitrile/water has now been investigated using the substrate 2,4-bis(dinitrophenyl)phosphate. The pH dependence of the catalytic rate revealed a non-symmetric bell-shaped profile, with a finite but non-zero rate at high pH. Unlike the traditional approach usually employed to analyse these bell-shaped profiles, the approach used here involved incorporating additional species which contribute to the overall activity. Employing this approach, we show that the complex has a k cat of 1.6 (±0.2) × 10-3 s-1, three kinetically relevant pK a values of 5.3, 6.2 and 8.4, with K M of 7.4 ± 0.6 mM. The kinetic parameters are similar to those reported for heterovalent PAP biomimetics. Additionally, it is observed that, unlike the enzyme, the oxidation state is not the determining factor for catalytic activity. Graphical Abstract: [Figure not available: see fulltext.]
KW - Binuclear metallohydrolases
KW - Biomimetics
KW - Iron complexes
KW - Phosphodiester-degrading enzyme
KW - Purple acid phosphatase
UR - https://www.scopus.com/pages/publications/79951555388
U2 - 10.1007/s00775-010-0696-0
DO - 10.1007/s00775-010-0696-0
M3 - Article
C2 - 20798967
AN - SCOPUS:79951555388
SN - 0949-8257
VL - 16
SP - 25
EP - 32
JO - Journal of Biological Inorganic Chemistry
JF - Journal of Biological Inorganic Chemistry
IS - 1
ER -