IN VITRO EFFECTS OF FLUORIDE ON TRICARBOXYLIC ACID CYCLE DEHYDROGENASES AND OXIDATIVE PHOSPHORYLATION: PART I

Abstract

Studies were conducted on the in vitro effect of fluoride on the succinic oxidase system utilizing mitochondria obtained from cauliflower. Preincubation of mitochondria with fluoride did not increase inhibition of succinic oxidase. Various other tricarboxylic acid cycle substrates were used to determine their sensitivity to fluoride; only succinate oxidation was affected. A series of succinate concentrations in the presence and in the absence of fluoride showed increased activity of succinic dehydrogenase, which indicated competitive inhibition. Various concentrations of phosphate in the absence of fluoride showed that phosphate had only slight effects on the succinic 2,6-dichlorophenolindophenol reductase component of the succinic oxidase system. In the absence of phosphate, various concentrations of fluoride showed an initial increase in activity followed by a decrease in activity of succinic 2,6-dichlorophenolindophenol reductase. In the presence of phosphate, fluoride caused marked inhibition of succinic 2,6-dichlorophenolindophenol reductase. It is believed that this inhibition results from an enzyme-fluorophosphate complex which has a lower dissociation constant than that of the enzyme-substrate complex. An oxidative phosphorylation study indicated that both respiration and phosphorylation were inhibited.