The Inhibition of Enolase by Fluoride in vitro

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Abstract
The activity of a commercial preparation of muscle enolase was determined photometrically. The sensitivity of the enzyme to fluoride and the kinetics of the inhibition was studied in the absence and in the presence of 5 mM phosphate. The effects of fluoride, magnesium, phosphate and fluorophosphate were investigated by introducing these ions alone or in combination in the assay medium during automatic recording. The inhibition of enolase in vitro started at 0.5 ppm fluoride in the presence of phosphate, and at 10 ppm in the absence of phosphate ions. The Lineweaver-Burk (1/V-1/[S]) and the Dixon (1/V-[F-])plots show that, in the presence of phosphate, the inhibition of enolase by fluoride is of the competitive type. In the absence of phosphate, the kinetics indicate a mechanism of inhibition identical to that found for enzymes without metal ion cofactors. When introduced in the assay medium during recording, fluoride produced a change of slope which was progressive and required 10-15 sec to be complete. The inhibition of enolase in the absence of phosphate, the results of the kinetic studies and those on the rapidity of the inhibitory action confirm that the inhibition of the enolase reaction is probably not caused by a purely inorganic complex.

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