The effects of cadmium on the p-nitrophenyl phosphatase and inorganic pyrophosphatase activities of alkaline phosphatase in developing hamster tooth germs

Abstract

p-Nitrophenyl phosphatase ( p-NPP-ase) and inorganic pyrophosphatase (PP i-ase) activities originate from the same alkaline phosphatase enzyme. Only the PP i-ase site has zinc (Zn 2+) as a cofactor. Cadmium (Cd 2+) in concentrations from 10 −5 mol/l upwards inhibited the PP i-ase activity, but did not inhibit the p-NPP-ase activity at all. In mineralizing tooth germs Cd 2+ may replace Zn 2+, thereby changing the specific stereoconfiguration in the active centre needed for PP i-ase activity, but not that for p-NPP-ase activity.