Photoaffinity labelling shows that Escherichia coli isocitrate dehydrogenase kinase/phosphatase contains a single ATP-binding site.

Ultraviolet irradiation of E.coli isocitrate dehydrogenase kinase/phosphatase in the presence of 8-azidoATP resulted in parallel losses of its kinase and phosphatase activities, and in covalent attachment of the reagent to the protein at a single site. ATP and ADP protected the two activities to similar extents. The data suggest that the activation of the phosphatase by adenine nucleotides results from binding of the nucleotides to the active site of the kinase.