Threonine deaminase from Salmonella typhimurium. II. The subunit structure.

Purified threonine deaminase of Salmonella typhimurium was found to be monodisperse and to have a molecular weight of 194,000. The protein, in 6 M guanidine HCI and 0.1 M P-mercaptoethanol, dissociates into polypeptide chains of molecular weight 48,500. Tryptic peptide analysis implies that the four component chains of the native enzyme are of identical amino acid sequence. L-Isoleucine and L-valine, which are allosteric effecters of this enzyme, have no effect on the sedimentation properties and do not produce detectable changes in the optical rotatory dispersion curve of the native enzyme.