The binding of nucleotides to pig heart nucleoside-diphosphate kinase was studied using Rose Bengal as an optical probe. ATP, in the absence of Mg2+, binds slowly to the enzyme, with a second order rate constant of about 3000 M−1·s−1, whereas in its presence the binding is much faster. This finding suggests the regulation of the nucleoside-diphosphate kinase activity by uncomplexed ATP, and that ATP binds normally to the enzyme via a metal ion bridge.
