J. Biochem, 1977, Vol. 81, No. 5 1455-1463
© 1977 Japanese Biochemical Society
research-article |
Effect of Halide Anions on the Binding of FAD to D-Amino Acid Oxidase and the Tryptophanyl Fluorescence of the Apoenzyme
*Department of Biochemistry, Medical School, Osaka University Kita-ku, Osaka, Osaka 530
**Department of Physicochemical Physiology, Medical School, Osaka University Kita-ku, Osaka, Osaka 530
The quenching of tryptophanyl fluorescence of native and denatured D-amino acid oxidase from hog kidney was measured. About 60% of the tryptophanyl fluorescence of the native .apoenzyme was quenched by iodide at pH 8.3, and 25°C. All of the tryptophanyl fluorescence of the apoenzyme in 6 M guanidine hydrochloride was quenched. The tryptophanyl fluorescence quenching of the holoenzyme by 1-methyl nicotinamide chloride was low in comparison with that of the apoenzyme. These results of the quenching experiments are discussed based on the intermolecular collision quenching mechanism.
By measuring the fluorescence intensities of the tryptophanyl residues and FAD of the .holoenzyme solution, and the fluorescence polarization of the holoenzyme solution containing halide anions such as iodide, bromide, chloride, or fluoride, we found that FAD dissociates from the holoenzyme in the presence of iodide, bromide, or chloride, and the ability to dissociate FAD from the holoenzyme decreases in order iodide, bromide, and chloride. However, fluoride seems to enhance the association reaction of FAD with the apoenzyme. These results were consistent with the visible absorption spectra and derivative spectra of free FAD and the holoenzyme in the presence and absence of halide anions.