Threonine dehydrogenase (EC 1.1.1.103) is a β-NAD+ coenzyme dependent enzyme, from the group of short chain alcohol dehydrogenases. It is a key enzyme in L threonine catabolism in microorganisms and mammals. The enzyme catalyzes conversion of l-threonine to 2-amino-3 ketobutyrate, with simultaneous reduction of NAD+.