Kinetics of primary interaction of D-amino acid oxidase with its substrate

The formation of an initial enzyme-substrate complex of D-amino acid oxidase (D-amino acid: O2 oxidoreductase (deaminating), EC 1.4.3.3) and its substrate, D-alpha-aminobutyric acid, was studied kinetically at lower temperature and pH than their optima. The time course of the absorbance change at 516 nm in an anaerobic reaction was not exponential, but biphasic. The ratio of the rapidly reacting component to the slowly reacting one was decreased upon lowering of the temperature. The reaction rate of the rapidly reacting component depended on substrate concentration and gave a linear Arrhenius plot in the temperature range from -10 to +15 degrees C. The reaction rate of the slowly reacting component also depended on both substrate concentration and temperature. The rapidly reacting and slowly reacting components could be assigned to the substrate binding of the dimer and monomer, respectively, of this enzyme.