Phosphate ester cleavage promoted by a tetrameric iron(III) complex.
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 (H(3)HPBA) 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-CH(3)COO)(2)(μ-O)(μ-OH)(OH(2))(2)]ClO(4)·5H(2)O. 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.
Kantacha
Anob
A
Department of Chemistry, Faculty of Science, Thaksin University, 140 Tambon Koaroobchang, Muang, Songkhla, Thailand.
Buchholz
Rebecca
R
Smith
Sarah J
SJ
Schenk
Gerhard
G
Gahan
Lawrence R
LR
D000135:Acid Phosphatase / Q000737:chemistry / Q000378:metabolism; D032701:Biomimetics; D002384:Catalysis; D004952:Esters / Q000737:chemistry*; D005290:Ferric Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D006023:Glycoproteins / Q000737:chemistry / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D015394:Molecular Structure; D010710:Phosphates / Q000737:chemistry*
D004952:Esters; D005290:Ferric Compounds; D006023:Glycoproteins; D010710:Phosphates; C091137:purple acid phosphatase; D000135:Acid Phosphatase
Biochemistry. 1998 Aug 11;37(32):11223-31
9698368
Inorg Chem. 2002 Nov 4;41(22):5641-3
12401063
Inorg Chem. 2003 Jan 27;42(2):499-507
12693232
Dalton Trans. 2007 Nov 28;(44):5132-9
17985020
J Am Chem Soc. 2007 Jun 20;129(24):7486-7
17518469
J Biol Inorg Chem. 2007 Nov;12(8):1207-20
17701232
Chem Rev. 2005 Jun;105(6):1923-59
15941206
Chem Rev. 2006 Aug;106(8):3338-63
16895331
Inorg Chem. 2009 Aug 17;48(16):7905-21
19603814
J Biol Inorg Chem. 2008 Jan;13(1):139-55
17938975
Inorg Chem. 2002 Feb 25;41(4):913-22
11849094
J Biol Inorg Chem. 2005 Jun;10(4):319-32
15843985
Arch Biochem Biophys. 2005 Jul 15;439(2):154-64
15950921
Biochemistry. 1991 Aug 20;30(33):8187-94
1868093
Inorg Chem. 2002 Sep 9;41(18):4624-6
12206683
Inorg Chem. 2002 Dec 2;41(24):6474-87
12444793
Biochemistry. 2004 Aug 17;43(32):10387-92
15301537
Inorg Chem. 2002 Nov 4;41(22):5787-94
12401084
Plant Physiol Biochem. 2005 Jul;43(7):651-8
16023357
Arch Biochem Biophys. 2001 Oct 15;394(2):280-2
11594743
J Biol Chem. 1983 Mar 10;258(5):3166-72
6298226