Aspects of carbonic anhydrase and carbonate content during mineralization of the rat enamel.

We examined carbonic anhydrase and carbonate content in developing dental enamel to clarify some problems in connection with the initial mineralization. Two-dimensional electrophoretic analysis showed that the type of carbonic anhydrase isoenzyme in developing enamel tissue was a low-activity form. A relatively high activity of carbonic anhydrase was detected in the developing enamel of rat lower incisors. We also determined that the content rate of carbonic anhydrase accounts for about 4% of the total matrix proteins of early developing enamel. A remarkable reduction of carbonic anhydrase activity occurred at the maturation stage, and then disappeared in the fully matured enamel. The carbonate content also decreased gradually, showing a parallel profile to that of carbonic anhydrase activity, from 3.5% to 1.9% in mineral phase. From the present study, we proposed that carbonic anhydrase in the initial site of mineralization may act as a trigger for the crystal nucleation by supplying the carbonate ions into the precursor mineral at the early stage of crystal development.