Studies on the Mechanism of Action of 2-Keto-3-deoxy-l-arabonate Dehydratase

When the enzymic conversion of 3-deoxy-2-oxo-l-arabonate to 2,5-dioxovalerate is carried out in HTO or D2O, isotopic hydrogen is incorporated at C-3 and C-4 of the product. In D2O, 1 deuterium atom is incorporated stereospecifically at each position. Treatment of the enzyme with NaBH4 in the presence of substrate leads to inactivation of the enzyme and to covalent binding of 1 mole of substrate to 1 mole of enzyme. It was therefore concluded that the substrate and enzyme interact to form a Schiff base. A mechanism for the over-all reaction is proposed in which the enzyme-substrate Schiff base participates and which accounts for the observed isotope incorporation.