Characterization of the fluoroacetate detoxication enzymes of rat liver cytosol

Two forms of fluoroacetate-specific defluorinase (FSD) were purified from rat hepatic cytosol. The first form, FSD1 (molecular weight 38 kDa), contained 81% of the total cytosolic fluoroacetate defluorination activity and did not bind to the glutathione-affinity, orange A or mono P columns used in the purification procedures. The second form, FSD2 (molecular weight 27 kDa), contained only 13% of the fluoroacetate defluorination activity, had a pI = 7.8, and exhibited a high glutathione S-transferase (GST)-like activity towards dichloroacetic acid. The FSD1 proteins were identified from peptide mass data and best matched with rat sorbitol dehydrogenase (SDH) (short form), although pure sheep liver SDH enzyme did not possess defluorination activity when subsequently investigated. The FSD2 protein was identified from peptide mass data and best matched with the amino acid sequence of mouse and human Zeta 1 of glutathione S-transferase (GSTZ1) and showed a high GSTZ1 specific activity. This study suggests that the major FSD component (FSD1) represents a new and unique dehalogenating or dehydrogenating enzyme present in rat liver cytosol. The minor FSD component (FSD2) is due to the GSTZ1 present in rat liver cytosol. However, it is not yet clear that FSD1 is indeed SDH and FSD2 is indeed GSTZ1, due to sequence homology being less than 60 and 45%, respectively.