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Kinetics of the low pH decolorization of azurin
Authors:Russell Timkovich
Affiliation:Department of Chemistry, Illinois Institute of Technology, U.S.A.
Abstract:Reaction rates were measured for the low pH-induced Cu ligand modification of azurins from Pseudomonas aeruginosa and Alcaligenes faecalis. Loss of the intense absorption band at 625 nm obeyed a rate law:
/></figure> where Az is the concentration of azurin in its native oxidized form possessing the 625 nm band. For <em>Pseudomonas aeruginosa</em> at 25°C, <em>n</em> = 1 and <em>k</em> = 4.0 × 10<sup>-2</sup> sec<sup>-1</sup> M<sup>-1</sup> in citrate buffer but 1.2 × 10<sup>-2</sup> sec<sup>-1</sup> M<sup>-1</sup> in phosphate buffer. For <em>Alcaligenes faecalis, n</em> = 3 and <em>k</em> = 1.5 × 10<sup>4</sup> sec<sup>-1</sup> M<sup>-3</sup> in citrate and 2.6 × 10<sup>3</sup> sec<sup>-1</sup> M<sup>-3</sup> in phosphate. In equilibrium experiments on <em>Alcaligenes faecalis</em> azurin in citrate buffer, the pH-dependent change to the low pH form exhibited an apparent transition pK of 3.1. The form of the rate law implies a mechanistic scheme that contains fast equilibrium protonation steps prior to a rate limiting ligand rearrangement.</td> </tr> <tr> <td align=
Keywords:Address reprint requests to: Russell Timkovich   Department of Chemistry   Illinois Institute of Technology   Chicago   IL 60616   USA
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