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- Title
The reaction mechanism of the Ga(III)Zn(II) derivative of uteroferrin and corresponding biomimetics.
- Authors
Smith, Sarah J.; Casellato, Annelise; Hadler, Kieran S.; Mitić, Nataša; Riley, Mark J.; Bortoluzzi, Adailton J.; Szpoganicz, Bruno; Schenk, Gerhard; Neves, Ademir; Gahan, Lawrence R.
- Abstract
Purple acid phosphatase from pig uterine fluid (uteroferrin), a representative of the diverse family of binuclear metallohydrolases, requires a heterovalent Fe(III)Fe(II) center for catalytic activity. The active-site structure and reaction mechanism of this enzyme were probed with a combination of methods including metal ion replacement and biomimetic studies. Specifically, the asymmetric ligand 2-bis{[(2-pyridylmethyl)-aminomethyl]-6-[(2-hydroxybenzyl)(2-pyridylmethyl)]aminomethyl}-4-methylphenol and two symmetric analogues that contain the softer and harder sites of the asymmetric unit were employed to assess the site selectivity of the trivalent and divalent metal ions using 71Ga NMR, mass spectrometry and X-ray crystallography. An exclusive preference of the harder site of the asymmetric ligand for the trivalent metal ion was observed. Comparison of the reactivities of the biomimetics with Ga(III)Zn(II) and Fe(III)Zn(II) centers indicates a higher turnover for the former, suggesting that the M(III)-bound hydroxide acts as the reaction-initiating nucleophile. Catalytically active Ga(III)Zn(II) and Fe(III)Zn(II) derivatives were also generated in the active site of uteroferrin. As in the case of the biomimetics, the Ga(III) derivative has increased reactivity, and a comparison of the pH dependence of the catalytic parameters of native uteroferrin and its metal ion derivatives supports a flexible mechanistic strategy whereby both the μ-(hydr)oxide and the terminal M(III)-bound hydroxide can act as nucleophiles, depending on the metal ion composition, the geometry of the second coordination sphere and the substrate.
- Subjects
CRYSTALLOGRAPHY; BIOMIMETIC chemicals; PARASYMPATHOMIMETIC agents; SYMPATHOMIMETIC agents; INTERMEDIATES (Chemistry); PROPERTIES of matter; HYDROGEN-ion concentration
- Publication
Journal of Biological Inorganic Chemistry (JBIC), 2007, Vol 12, Issue 8, p1207
- ISSN
0949-8257
- Publication type
Article
- DOI
10.1007/s00775-007-0286-y