It has been suggested that the toxicity of fluoroacetate is due to the enzymic synthesis of a fluorotricarboxylic acid, which ‘jams’ the tricarboxylic acid cycle at the citrate stage. This communication presents the proof of this hypothesis. The inhibitory substance for citrate metabolism synthesized by enzymic action from fluoroacetate has been isolated as a compound in crystalline form of great potency. Under the conditions of test it inhibits the disappearance of approximately 300 times its weight of citric acid in 30 min. The final isolation involved a separation from citric acid by the use of ion-exchange resin, and fractional extraction with ether. It is a monofluorotricarboxylic acid, as shown by its migration on a paper chromatogram, by its fluorine content (estimated spectrochemically), and by its titration curve. It does not give the colour reaction with sodium sulphide for pentabromacetone produced from citric acid by the usual methods. It gives an infra-red band which may be expected from a C-F bond. By a process of exclusion, it is considered to be a fluorocitric acid; a final decision must await synthesis.
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