L-threonine dehydrogenase of Escherichia coli K-12

Abstract

SummaryA rapid method for purifying L-threonine dehydrogenase from Escherichia coli K-12 cells, grown on a medium containing L-threonine as carbon source, has been developed. The procedure consists of three fractionation steps of which the last is adsorption and elution of the enzyme from a column of Blue dextran-Sepharose. Homogeneous and stable samples of the dehydrogenase are obtained. L-Threonine dehydrogenase of E. coli has an average molecular weight of 140,000 and consists of 4 identical or nearly identical subunits. Km values for L-threonine and NAD[circle plus operator] are 1.4 mM and 0.19 mM, respectively; several substrate and coenzyme analogs are also active. The pH optimum is 10.3 and Mn++ stimulates dehydrogenase activity. Other properties of the pure enzyme have been established.