EFFECT OF BOUND PHOSPHOPROTEINS AND OTHER ORGANIC-PHOSPHATES ON ALKALINE PHOSPHATASE-INDUCED MINERALIZATION OF COLLAGENOUS MATRICES IN-VITRO

The aim of the present study was to determine to what extent the rate at which collagen mineralizes correlates with the amount and nature of bound phosphate groups. Sheets of collagen prepared from demineralize d bovine dentin or cortical bone were complexed with various concentra tions of phosphoserine [(P)Ser] or rat dentin phosphoproteins (PP; low ly or highly phosphorylated PP, LPP or HPP). Alternatively, phosphate groups were removed from the collagenous carrier material by treatment with phosphatases. Mineralization was achieved by incubation in cultu re medium supplemented with Ca-45, alkaline phosphatase and 10 mM beta -glycerophosphate. The sheets were monitored for uptake of Ca-45 and l ag times calculated and plotted against the amount of bound phosphate. It was observed that dephosphorylation of the carrier causes an incre ase in lag time and that rat PP decreases lag times in a concentration -dependent way. HPP were more effective than LPP. (P)Ser or other smal l organic P-containing molecules had hardly any influence on lag time. It is concluded that next to the amount of bound phosphate, the natur e of phosphorylated substances has considerable influence on the rate of mineralization of a collagenous carrier.