XB-ART-18578Protein Sci 1996 Feb 01;52:248-53.
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Identification of the residues responsible for the alkaline inhibition of Cu,Zn superoxide dismutase: a site-directed mutagenesis approach.
The catalytic rate of wild type, two single (Lys 120-->Leu, Lys 134-->Thr), and one double (Lys 120-->Leu-Lys 134-->Thr) mutants of Xenopus laevis B Cu,Zn superoxide dismutase has been studied by pulse radiolysis as a function of pH. The pH dependence curve of the wild-type enzyme can be deconvoluted by two deprotonation equilibria, at pH 9.3 (pK1) and at pH 11.3 (pK2). Catalytic rate measurements on single and double mutants indicate that pK1 is mainly due to the deprotonation of Lys 120 and Lys 134, with only a minor contribution from other surface basic residues, whereas pK2 is due to titration of the invariant Arg 141, likely coupled to deprotonation of the copper-bound water molecule. Accordingly, Brownian dynamics simulations carried out as a function of pH reproduce well the pH dependence of the catalytic rate, when the experimentally determined pKs are assigned to Lys 120, Lys 134, and Arg 141.
PubMed ID: 8745402
PMC ID: PMC2143332
Article link: Protein Sci
Species referenced: Xenopus laevis
Genes referenced: pklr prok1 prok2
References [+] :
Argese, Electrostatic control of the rate-determining step of the copper, zinc superoxide dismutase catalytic reaction. 1987, Pubmed