pH studies on the mechanism of the pyridoxal phosphate-dependent dialkylglycine decarboxylase.

摘要: The pH dependence of the steady-state kinetic parameters for dialkylglycine decarboxylase-catalyzed decarboxylation-dependent transamination between 2-aminoisobutyrate (AIB) and pyruvate is presented. methylation DTNB modification reactions, spectroscopic properties, used to augment assignment pKa's specific ionizations. coincidence pKa values (∼7.4) observed in kcat/KAIB, 1/KAIB, Kis pyruvate, KPLP, absorbance fluorescence titrations demonstrates that AIB not a sticky substrate. It furthermore suggests decarboxylation step, or conformational isomerization preceding it, limits rate overall catalytic cycle. Coexisting, kinetically distinguishable conformers DGD-PLP, originating from an alkali metal ion binding site, were previously demonstrated at 8.2 DGD-PLP (Zhou, X., Toney, M. D. Biochemistry 37, 5761−5769). value ∼8.8 kcat, Kd K+, spectrometric titrati...