Relationship of inorganic pyrophosphatase and alkaline phosphatase activities in hamster molars.

Abstract

1. Some properties of inorganic pyrophosphatase (PPi-ase) and alkaline phosphatase (p-NPP-ase) in the molars of 3-day-old hamsters are described. 2. The pH optimum for inorganic pyrophosphatase is 8.7, for alkaline phosphatase 10.3. 3. The ratio of Mg2+: PPi for optimal inorganic pyrophosphatase activity is 1∶1. There is no clear optimal ratio in the case of p-NPP-ase. 4. The ratio of the enzymic activity of the membrane bound fraction to the soluble fraction is 3.4∶1 (S.E. 0.37) for PPi-ase and 3.2∶1 (S.E. 0.42) for p-NPP-ase activity. 5. A mutual substrate competition for the pyrophosphatase and alkaline phosphatase activities is demonstrated. 6. Both enzymatic activities have similar temperature-activity curves with the same maximum at 38°. 7. Microdissection of ameloblasts and stratum intermedium cells from lyophilized sections showed the same activity ratio for both enzyme activities: Stratum intermedium: ameloblasts for PPi-ase 4.7 (S. E. 0.93) and for p-NPP-ase 4.2 (S.E. 0.79). 8. High-voltage, free-flowing electrophoresis of the homogenate gave equal distribution patterns for p-NPP-ase and PPi-ase greatly different from the protein distribution pattern. 9. It is concluded that the two activities are due to the same enzyme.