PMID: 2906936Nov 1, 1988

Complex formation between anionic semiquinoid form of a flavoenzyme D-amino acid oxidase and ligands. Stabilizing mechanism of anionic semiquinoid flavoenzyme

Journal of Biochemistry
Y NishinaK Shiga

Abstract

Picolinate binds to the anionic semiquinoid form of D-amino acid oxidase (DAO), and the complex formed has a broad absorption band in the long-wavelength region extending beyond 800 nm, which is reminiscent of a charge transfer interaction. The binding has a stoichiometry of 1:1 with respect to the enzyme. The dissociation constant at 25 degrees C was 30 microM at pH 7.0. The pH dependence (pH 7.0-8.3) of the dissociation constant indicates that one proton is associated with the complex formation, and suggests that picolinate able to bind to the anionic semiquinoid enzyme is in the cationic form protonated at the nitrogen atom. By adding dithionite to the oxidized DAO solution containing pyruvate and various amines, a similar anionic semiquinoid DAO complex having a broad long-wavelength absorption band, appeared. Resonance Raman spectra with excitation at 623.8 nm of the anionic semiquinoid DAO complex formed in the presence of pyruvate and methylamine indicate that the complex consists of the anionic semiquinoid DAO and N-methyl-alpha-iminopropionate produced from pyruvate and methylamine, and that the imino group must be protonated. This supports the proposal that the presence of a positively charged group in the vicinity of...Continue Reading

Related Concepts

Picolinic acid, sodium salt
D-Amino Acid Dehydrogenase
Sodium Dithionite
Enzyme Stability
Hydrogen-Ion Concentration
Ligands
Oxidation-Reduction
Dioxygen
Picolinic Acids
Spectrometry

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