D-asparatate oxidase in the thyroid gland.

D-Aspartate oxidase was isolated from the pig thyroid gland and purified over 600 times. The enzyme was obtained in an inactive form of apoenzyme and was activated by FAD. It was specific towards the D-form of aspartic acid, had no effect on the L-form, and was also inactive towards other monocarboxlyic D-amino acids. The enzyme was only slightly active towards D-glutamate. The Michaelis constant based on the Lineaweaver-Burk plot was 5 mmol/l. The optimum pH was 8.7. D-Aspartate oxidase was inhibited by KCN in concentrations varying from 0.05 to 1 mmol/l. The biological role of this enzyme in the thyroid gland is discussed.