Fluoroacetates

Abstract: There is need in physiology for further convincing instances of the connexion of biochemical schemes based upon enzyme research with in vivo events in the living organism, in order to constitute the bridge between biochemistry and physiology. Up to the present, examples have been confined to the intermediary metabolism of pyruvate and vitamin B1, to the effect of some narcotics, and to the enzyme cholinesterase. In this paper, we give an account of another important bridge, based upon the formation of citrate in vivo by injection of the poison fluoroacetate (CH2F. COO-). Since the C-F bond is very stable (Swarts, 1896) this compound cannot combine with SR groups as happens with the other halogen compounds bromo or iodo acetate. According to a prominent biochemical scheme for the terminal stages of pyruvate utilization, as also of the oxidation of fatty acids, degradation occurs by synthesis from oxaloacetate and a 2-carbon active fragment of a 6-carbon tricarboxylic acid followed by subsequent degradation to a 5-carbon and then a 4-carbon dicarboxylic acid. In one turn of this cycle, known as the 'tricarboxylic acid' cycle (Krebs, 1943), oxidation of 1 molecule of pyruvate takes place. On the basis of enzyme experiments in vitro on homogenates of guinea-pig kidney freed from residual substrates by centrifuging, Peters, 1948 and Liebecq & Peters, 1948, 1949 have advanced the working hypothesis that fluoroacetate can be activated in intermediary metabolism like acetate, and so built with oxaloacetate into a 6-carbon acid in the citric acid series; the foreign fluoro acid then 'jams' the cycle, leading to accumulation of citrate at this stage. The 'jamming' hypothesis explained the accumulation of citrate found by Liebecq & Peters in their kidney preparations in the presence of the substrates fumarate or fumarate + pyruvate, preparations which normally oxidize added citrate well. The hypothesis is consistent also with the earlier idea of Bartlett & Barron (1947) that fluoroacetate competed with acetate for an enzymic