Threonine Deaminase from Salmonella typhimurium

Abstract

Abstract Threonine deaminase (l-threonine hydrolyase deaminating, EC 4.2.1.16), molecular weight 194,000, was dissociated into stable intermediate substructures, molecular weight 94,000, by resolving the enzyme of its cofactor, pyridoxal 5'-monophosphate. The intermediate substructures were catalytically inactive and were found to be composed of two of the four identical polypeptide chains which constitute the native tetrameric enzyme. It was determined that the native enzyme contains two disulfide bonds and that these bonds are formed between the subunits of the apodimers. Addition of pyridoxal 5'-monophosphate to a mixture of the apodimers promotes a reassociation into a tetrameric form and a regain of enzymic activity. The reconstituted enzyme binds only 2 molecules of pyridoxal phosphate and its regulatory properties are the same as the native enzyme. The structure-function relationships with respect to the protomeric nature of this enzyme are discussed.