Cofactor identification of threonine-serine dehydratase from sheep liver.
L-Threonine-serine dehydratase catalyzes the conversion of L-threonine and L-serine to alpha-ketobutyric acid and pyruvate, respectively. The enzyme has been purified to homogeneity from extracts of sheep liver. In the past, various cofactors have been suggested for threonine dehydratase from both prokaryotic and eukaryotic tissue. While some direct evidence for the presence of pyriodoxal 5'-phosphate in impure preparations is present in the literature no direct evidence for the cofactor in homogeneous dehydrogenase from mammalian tissue has been reported. The threonine dehydratase of sheep liver has been obtained in a homogeneous form and a spectral study provides clear evidence for the presence of pyridoxal 5'-phosphate. Both the physical properties of homogeneous threonine dehydratase and a study of spectral properties of its cofactor are reported in this communication.