The metabolism of fluoroacetate in lettuce

Abstract

1. Whole lettuce plants were incubated with (1) [1-14C]acetate, (2) fluoroacetate followed by [1-14C]acetate, (3) fluoro[1-14C]acetate, (4) fluoro[2-14C]acetate or (5) S-carboxy[14C]methylglutathione. 2. Fluoroacetate did not affect the expiration of 14CO2 from [1-14C]acetate and only a small amount of 14CO2 was produced from either fluoro[1-14C]-acetate or fluoro[2-14C]acetate in 43h. 3. Fluoroacetate at 50mg/kg wet wt. doubled the plant citrate concentration after 43h incubation, and depending on the age and size of the plant 50–100% of the compound was metabolized. 4. With both fluoro[1-14C]acetate and fluoro[2-14C]acetate all the radioactivity except that in the CO2 was found in the water-soluble acid fraction. About 2% was in fluorocitrate and the remainder, apart from unchanged fluoroacetate, was in a number of compounds devoid of fluorine but containing nitrogen and sulphur. These were peptide-like and could be separated by chromatography on an amino acid analyser. 5. Identical compounds were obtained from the spontaneous reaction between iodo[2-14C]acetate and glutathione, the major product being S-carboxymethylglutathione. 6. S-Carboxymethylcysteine was also isolated and its mass spectrum compared with a commercial sample. 7. Reaction rates of all the monohaloacetates with glutathione were studied at pH7 at 25°C. No reaction was observed with fluoroacetate. 8. The metabolism of fluoroacetate by lettuce is discussed in relation to that of aliphatic and aromatic halogen compounds, including fluoroacetate, by mammalian liver and to the metabolism of fluoroacetate by different plants reported by other workers.