Phosphate triester hydrolysis promoted by an N2S(thiolate)Zn complex: mechanistic implications for the metal-dependent reactivity of peptide deformylase.
The zinc(II) complex (PATH)ZnOH, where PATH is an N2S(thiolate) ligand, has been investigated for its ability to promote the hydrolysis of the phosphate triester tris(4-nitrophenyl) phosphate (TNP). The hydrolysis of TNP was examined as a function of PATH-zinc(II) complex concentration, substrate concentration, and pH in a water/ethanol mixture (66:33 v/v) at 25 degrees C. The reaction is first order in both zinc(II) complex and substrate, and the second-order rate constants were derived from linear plots of the observed pseudo-first-order rate constants versus zinc complex concentration at different pH values. A pH-rate profile yielded a kinetic pK(a) of 8.52(5) for the zinc-bound water molecule and a pH-independent rate constant of 16.1(7) M(-1) s(-1). Temperature-dependent studies showed linear Eyring behavior, yielding the activation parameters DeltaH++ = 36.9(1) kJ mol(-1) and DeltaS++ = -106.7(4) J mol(-1) K(-1). Interpretation of the kinetic data leads to the conclusion that hydrolysis of TNP takes place through a hybrid mechanism, in which the metal center plays a dual role of providing a nucleophilic hydroxide and activating the substrate through a Lewis acid effect. The synthesis and structural characterization of the related nickel(II) and iron(II) complexes [(PATH)2Ni2]Br2 (2) and (PATH)2Fe2Cl2 (3) are also described. Taken together, these data suggest a possible explanation for the low reactivity of the zinc(II) form of peptide deformylase as compared to the iron(II) form.
Goldberg
David P
DP
Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA. dpg@jhu.edu
diTargiani
Robert C
RC
Namuswe
Frances
F
Minnihan
Ellen C
EC
Chang
SeChin
S
Zakharov
Lev N
LN
Rheingold
Arnold L
AL
D000581:Amidohydrolases / Q000378:metabolism*; D018360:Crystallography, X-Ray; D006868:Hydrolysis; D007700:Kinetics; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000737:chemistry*; D010756:Phosphoric Acids / Q000737:chemistry*; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013816:Thermodynamics; D015032:Zinc / Q000737:chemistry*
C511541:(2-methyl-1-(methyl-(2-pyridin-2-ylethyl)amino)propane-2-thiolate)zinc(II); D009942:Organometallic Compounds; D010756:Phosphoric Acids; D013438:Sulfhydryl Compounds; D000581:Amidohydrolases; C084507:peptide deformylase; D015032:Zinc