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  • Title: Functional properties of beta-galactosidase from mutant strain 13 PO of Escherichia coli.
    Author: Deschavanne PJ, Viratelle OM, Yon JM.
    Journal: Proc Natl Acad Sci U S A; 1978 Apr; 75(4):1892-6. PubMed ID: 25441.
    Abstract:
    The functional properties of CZP protein, a mutant deriving from wild-type beta-galactosidase (beta-D-galactoside galactohydrolase; EC 3.2.1.23) by a point mutation, were investigated. A large decrease of the specificity, as evaluated by the kcat/Km ratio, was observed, principally originated by a weaker binding of the substrates. The catalytic constants, whose values are strongly affected by the presence of divalent cations, were smaller or larger for mutant enzyme than for wild-type enzyme, depending upon the experimental conditions. Analysis of the kinetic pathway indicates, with some substrates, a change in the limiting step for the mutant enzyme compared to the wild type. Because the k'3 step is rate limiting for hydrolysis of p-nitrophenyl-beta-D-galactoside by the mutant enzyme in the absence of Mg2+ and its value is relatively small, it is possible to observe a burst of p-nitrophenol during hydrolysis. This provides conclusive evidence for the occurrence of a two-step mechanism, with a sequential release of the products.
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