Inhibition of enzymatic hydrolysis of end-phosphate DNA by iridium chlorocomplexes

The enzymatic hydrolysis of end-phosphate DNA by calf intestine alkaline phosphatase is inhibited by iridium chlorocomplexes. The inhibitory effect is strongly influenced by the chemical form of iridium. While hexachloroiridate (IV) and hexachloroiridite (III) strongly inhibit the enzymatic activity of calf intestine alkaline phosphatase no inhibitory effect was observed when these chlorocomplexes were previously irradiated by light and transformed to their photochemical reaction products. Evidence is presented which suggests that the noncompetitive and irreversible inhibitory effect was due to an effective interaction of iridium with the protein without release of its metal constituent at a very low concentration of enzyme. The protective effects of various chemicals on the inhibitory action was also briefly investigated.