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Rods with a cross section of 3 mm2 were prepared from the labial surface of premolars extracted either 0.5, 1.5 or 3.5 years after eruption. Enamel slices with a thickness of 100 μm were cut from these rods at a distance of 100 μm apart from each other. The infrared spectra of these slices showed that the carbonate and HPO42− content of enamel increase with depth, whereas the A-type CO32− and OH− content decrease with depth. A possible involvement of these minor components in posteruptive maturation could not be detected.

Inorganic pyrophosphatase contains both Zn2+ and Co2+ in the active center. The highest activity of the enzyme was obtained in the Zn2+ form. EDTA, diphosphonates and L-ascorbic acid are able to inhibit PPi-ase by complexing Zn2+ and Co2+.

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.

A rapid 3-step method is given to purify partially hamster molar alkaline phosphatase. Molecular weight was 50,200 and isoelectric point 3.7. The alkaline phosphatases in the mesenchymal and ectodermal parts of the tooth are probably identical.