Abstract
1. Washed-cell suspensions of Escherichia coli, incubated at the optimum pH of 6·4 and with a saturating substrate concentration of approx. 10mm, convert dl-1-aminopropan-2-ol into aminoacetone at a rate of approx. 4·0mμmoles/mg. dry wt. of cells/min. at 30°. 2. Mg2+, Mn2+, Co2+, Zn2+, Ca2+, K+ and NH4+, as sulphates, and EDTA have no effect on this rate, although Cu2+ inhibits and Fe2+ activates to some extent. 3. Conditions of growth markedly affect the rate of aminoacetone production by cell suspensions. 4. Dialysed cell-free extracts of E. coli exhibit 1-aminopropan-2-ol-dehydrogenase activity, the enzyme having optimum activity at pH7·0, a requirement for NAD+ and K+, and a Km for the amino alcohol substrate of 0·8mm, calculated for a single enantiomorph. 5. Under optimum conditions 1-aminopropan-2-ol dehydrogenase forms aminoacetone at rate of approx. 3·0mμmoles/mg. of protein/min. at 37°. The enzyme is only slightly inhibited by dl-3-hydroxybutyrate and dl-2-hydroxy-2-phenylethyl-amine. 6. l-Threonine-dehydrogenase activity is exhibited by both whole cells and cell-free extracts. Whole cells produce aminoacetone from l-threonine more slowly than they do from dl-1-aminopropan-2-ol, whereas the situation is reversed in cell-free extracts. Both kinetic evidence, and the fact that synthesis of 1-aminopropan-2-ol dehydrogenase, but not of threonine dehydrogenase, is repressed by compounds such as glucose and pyruvate, provide evidence that the amino alcohol is oxidized by a specific enyme. 7. The metabolic role of 1-aminopropan-2-ol dehydrogenase is discussed.
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