Changes in alkaline-phosphatase isoenzymes of hard tissue origin during facial development in the rat

Non-specific alkaline phosphatase (APase) activity was demonstrated histochemically in the hard-tissue-forming areas of the developing rat face from the 14th embryonic day. Isoenzyme distribution of APase was recorded by isoelectric focusing. Three APase isoenzyme bands with lower isoelectric points than adult forms were recorded. Inhibition studies with levamisole dexamisole, L-p-bromotetramisole, D-p-bromotetramisole, diphosphonates and urea showed the embryonic isoenzymes to have the same sensitivity as the adult forms except to urea. Heated to 56 degrees C, both embryonic and adult APase were rapidly inactivated. The differences between the embryonic and adult forms of APase may represent the expression of different gene loci or a difference in post-translational modification.