1. A sensitive fluorimetric procedure for the assay of d-amino acid oxidase has been developed. 2. The method depends on the formation of a fluorescent derivative, 2-hydroxy-3-methylquinoxaline, on condensation of pyruvate with o-phenylenediamine in acid medium. 3. 2-Hydroxy-3-methylquinoxaline fluoresces strongly in 50% (v/v) sulphuric acid after excitation at 375mmu. A single emission peak is observed at 480mmu. 4. Formation of the quinoxaline is dependent on time, temperature, acidity and relative concentration of reactants. 5. A particulate preparation from mouse kidney required FAD for optimum activity at pH8.5; K(m) was 3.8x10(-3)m; K(FAD) was 1.4x10(-7)m and the reaction was strongly inhibited by p-chloromercuribenzoate and phenylmercuric acetate. 6. Subcellular fractionation on a sucrose density gradient confirmed that the d-amino acid oxidase was localized on small granules.
Radioactive acetic anhydride was used to label casein, isinglass, egg white, and a pectic enzyme complex. The pectic enzyme was added to three different grape juices which were fermented, bentonite fined and filtered in an approximation of industrial practice. Three wines were fined using isinglass or egg white (red wines) or casein (white wines) applied at three rates each, and finished as above. Residual amounts of each additive were determined by scintillation counting of samples taken at each step. All of the pectic enzyme remained in the finished wines. Residual fining agents decreased with the application rate to levels showing much variation in the red wines and less in the whites.
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