Coexisting kinetically distinguishable forms of dialkylglycine decarboxylase engendered by alkali metal ions

Biochemistry
Xianzhi ZhouM D Toney

Abstract

The pyridoxal phosphate (PLP) dependent enzyme dialkylglycine decarboxylase (DGD) specifically binds alkali metal ions near the active site. Large ions (Rb+, K+) activate the enzyme while smaller ones (Na+, Li+) inhibit it. Crystallographic results have shown that DGD undergoes a metal ion size dependent structural switch [Hohenester, E., Keller, J. W., and Jansonius, J. N. (1994) Biochemistry 33, 13561], but no evidence for multiple conformations in crystalline DGD was obtained. Here, evidence is presented that DGD-K+ in solution exists in two conformations differing in catalytic competence. Initial rate traces for DGD-K+ exhibit a high degree of curvature due to decreasing activity over time. DGD remains tetrameric under the assay conditions as demonstrated by gel filtration experiments, arguing against the possibility of subunit dissociation as the source of activity loss. Likewise, the mass spectrum of DGD shows a single covalent form. A hysteretic model that assumes two slowly interconverting enzyme forms accounts well for the initial rate data when kinetic parameters from biphasic pre-steady-state kinetics are employed. The fit of the model to the data yields an estimate of 59 +/- 1% for the fast form. A cooperative model...Continue Reading

Citations

Feb 15, 2014·Journal of the American Chemical Society·Pavel A DubJohn C Gordon
Jun 15, 2011·Biochimica Et Biophysica Acta·Michael D Toney
Aug 22, 2016·Journal of Industrial Microbiology & Biotechnology·Wisarut PayoungkiattikunYasuhisa Asano
Nov 11, 1999·Journal of Molecular Biology·V N MalashkevichM D Toney
Jun 25, 2019·Dalton Transactions : an International Journal of Inorganic Chemistry·Levente G PapElliott Hulley

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