Studies of the N-bromosuccinimide inactivation of the enzyme rhodanese

The enzyme rhodanese (Thiosulfate : cyanide sulphurtransferase, EC 2.8.1.1) is rapidly inactivated by treatment with N-bromosuccinimide. Spectrophotometric titration and sodium dodecyl sulfate polyacrylamide gel electrophoresis show that neither tryptophan oxidation nor polypeptide chain cleavage can account for the inactivation. Sulfhydryl group assays using the colormetric reagent 5,5′-dituiobis(2-nitrobenzoic acid) after destruction of excess N-bromosuccinmide, indicate that approximately 2 sulfhydryl groups per enzyme molecule are lost. Further, rhodanese inactivated by N-bromosuccinimide can be reactivated (∼95%) by incubation with the substrate thiosulfate. It is postulated that N-bromosuccinimide inactivates rhodanese by inducing the formation of a disulfide bond involving the active site sulfhydryl group of the enzyme and a second sulfhydryl group which can be brought close to the active site in the flexible native structure.