Threonine dehydrogenase has been purified to apparent homogeneity from Klebsiella pneumoniae and Enterobacter aerogenes. Purification was achieved by sequential chromatography on DEAE ion exchange, Blue Sepharose affinity gel, and Toyopearl HW-55s gel filtration. The amino-terminus for the enzyme in both organisms has been sequenced and placed the enzyme from K. pneumoniae with a class of long chain alcohol dehydrogenase family. The subunit molecular mass was estimated as 38.8 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, while an apparent native molecular mass of 154 kDa was shown by gel filtration chromatography, suggesting a tetrameric structure. As for the enzyme from E. aerogenes, it is described as a possible dimer with a native molecular mass estimate of 104.5 kDa, and a subunit molecular mass estimate of 43.1 kDa. This enzyme showed homology to a group of alcohol dehydrogenase I family with a preference to propanol as a substrate
