The Enzymatic defluorination of fluoroacetate in mouse liver cytosol: The separation of defluorination activity from several glutathione S-transferases of mouse liver

The liberation of free fluoride ion from fluoroacetate (FAc) proceeds as an enzymecatalyzed dehalogenation reaction in the soluble fractions of several organs of the CFW Swiss mouse. Liver contained the highest FAc defluorinating activity. The enzyme activity in other organs decreased in the order kidney > lung > heart > testes. No activity was detected in the brain. Experiments were designed to characterize and identify the enzyme species responsible for FAc metabolism in liver. Enzyme activity was dependent on the concentration of glutathione (GSH) in the assay mixture, with maximal activity occurring above 5 mm. The dehalogenation of FAc had an apparent K_m of 7.0 mm when measured in the presence of a saturating concentration of GSH. An increase in the pH of the assay mixture enhanced fluoride release in both phosphate and borate buffer. The defluorination activity was reduced to negligible levels when stored for 24 h at 4 °C. The addition of either GSH, dithiothreitol, or 2-mercaptoethanol increased stability, with the latter providing protection for greater than 150 h at a concentration of 15 mm. DEAE anion-exchange chromatography separated the defluorinating activity from 90% of the soluble GSH S-transferase activity measured with 1-chloro-2,4-dinitrobenzene. FAc defluorination activity did not bind to a GSH affinity column which selectively separates it from a group of anionic GSH S-transferases. The GSH-dependent enzyme which dehalogenates FAc has unique properties and can be separated from the liver GSH S-transferases previously described in the literature.