Formation of D-1-amino-2-propanol from L-threonine by enzymes from Escherichia coli K-12

Escherichia coli K-12 cells contain two dehydrogenases which in sequence catalyze the net conversion of L-threonine to the D-isomer of 1-amino-2-propanol. These two enzymes are L-threonine dehydrogenase (L-threonine + NAD⁺ → aminoacetone + CO₂ + NADH + H⁺) and D-1-amino-2-propanol dehydrogenase (aminoacetone + NADH + H⁺D-1-amino-2-propanol + NAD⁺). Each enzyme has been obtained in purified form free of the other; the nature of the reaction catalyzed by the latter dehydrogenase alone and in a coupled system with the former enzyme has been studied. The results provide an explanation on the enzymological level for the utilization of L-threonine by cell suspensions of certain microorganisms for the biosynthesis of the D-1-amino-2-propanol moiety of Vitamin B₁₂.