Phosphate ester cleavage promoted by a tetrameric iron(III) complex.

Area of Science:

• Bioinorganic Chemistry
• Enzyme Mimicry
• Metallohydrolases

Background:

• Purple acid phosphatases (PAPs) are unique binuclear metallohydrolases requiring a heterovalent active site for catalysis.
• Biomimetic design of PAPs focuses on ligands that replicate the enzyme's active site donor atoms and metal ion discrimination.
• The ligand H(3)HPBA mimics PAP active site donors, but its iron(III) complex forms a tetramer.

Purpose of the Study:

• To investigate the phosphoesterase-like activity of the iron(III) complex of H(3)HPBA.
• To analyze the pH dependence of the catalytic rate using a novel approach incorporating additional contributing species.
• To compare the kinetic parameters of the biomimetic complex with those of natural PAPs.

Main Methods:

• Synthesis and characterization of the iron(III) complex of H(3)HPBA.
• Enzymatic activity assay using 2,4-bis(dinitrophenyl)phosphate as substrate in acetonitrile/water.
• Kinetic analysis of pH-dependent catalytic rates, employing a model that accounts for multiple active species.

Main Results:

• The iron(III) complex exhibited phosphoesterase-like activity with a k(cat) of 1.6 (±0.2) × 10(-3) s(-1).
• Kinetic analysis revealed three pK(a) values (5.3, 6.2, 8.4) and a K(M) of 7.4 ± 0.6 mM.
• The observed kinetic parameters are comparable to those of other heterovalent PAP biomimetics.

Conclusions:

• The H(3)HPBA iron(III) complex demonstrates functional biomimicry of PAPs.
• The catalytic activity is not solely determined by the metal oxidation state, unlike the native enzyme.
• The study highlights a more comprehensive approach to analyzing pH-dependent enzyme kinetics.