Fluoride alters casein kinase II and alkaline phosphatase activity in vitro with potential implications for dentine mineralization

Dentine phosphoprotein (DPP), a major non-collagenous acidic protein of den tine, undergoes altered phosphorylation in vivo in the presence of high flu oride concentrations. This has major implications for the altered mineraliz ation patterns found during fluorosis. In dentine. casein kinase II is invo lved in phosphorylating DPP, and alkaline phosphatase (ALP) is ascribed rol es in the dephosphorylation of DPP, increasing the inorganic phosphate at t he mineralization front and the removal of pyrophosphate. Here the influenc e of fluoride in vitro on the activity of purified casein kinase II and ALP and its relation to altered patterns of mineralization were examined. Kine tic analysis showed that casein kinase II activity was completely inhibited at 0.04 M NaF. V-max when compared to the control assay was significantly decreased (P < 0.0001) between concentrations 4 x 10(-4)-4 x 10(-8)M NaF. S ignificant changes to the K-m (P < 0.0001) were also observed. ALP activity was inhibited by NaF (0.09-9 x 10(-8)M), with V-max significantly decrease d (P < 0.0001) at 0.09 M NaF. Alterations in the activity of these enzymes in the presence of fluoride may in part explain the decreased phosphorylati on observed in DPP isolated from fluorotic dentine and may aid understandin g of the altered matrix mediated mineralization patterns found during fluor osis. (C) 2001 Elsevier Science Ltd. All rights reserved.