Kinetics of heterogeneous isotopic exchange of [8-3H]adenosine phosphates with hydrogen

The kinetics is studied of the reverse catalytic heterogeneous isotopic exchange between gaseous hydrogen and tritium-labelled nucleotides of the adenine group. Studied were the effects of the amount and properties of the catalyst, pH of the medium and of the concentration of reactants, on the value of the isotopic exchange rate constant (r) of adenine nucleotides. The 10% PdO/BaSO4 catalyst was found to be the most active with regard to the studied reaction. At the pH range 8-10, the value of r increased in the sequence AMP<ADP<ATP<cAMP. At low nucleotide concentrations the observed isotopic exchange rate constants were not dependent on nucleotide concentration. If, however, the concentration exceeded a certain limit, the value of r began to drop. In heterogeneous exchange, r dropped with increasing pH. This is due to the reactibility of different ion forms of nucleotides of the adenine group. (author). 5 figs., 1 tab., 6 refs