Inhibition of rat liver rhodanese by di-, tricarboxylic, and alpha-keto acids.

Rat liver rhodanese [EC 2.8.1.1] purified by ammonium sulfate fractionation, CM-cellulose and Sephadex G-200 chromatography yielded two active fractions (I & II). Their molecular weights were estimated to be 1.75 X 10(4) (I) and 1.26 X 10(4) (II) by the gel filtration method. Kinetic studies revealed that Fraction I rat liver rhodanese catalyzes thiocyanate formation from thiosulfate and cyanide by a double displacement mechanism. Carboxylic acids such as DL-isocitric, citric malic, pyruvic, and oxaloacetic acid were competitive inhibitors with respect to thiosulfate, whereas fumaric, succinic, and alpha-ketoglutaric acids were noncompetitive inhibitors with respect ot thiosulfate. Incubation of mitochondria with sulfate and alpha-ketoglutaric acid caused a significant decrease in rhodanese activity.