Vitamin D-dependent Calcium-binding Protein

6- and %fold, respectively, during the third trimester of pregnancy in parallel with the fetal demands for skeletal mineral. Studies of in vitro protein synthesis indicated that CaBP was synthesized by placental tissue. Slices of mouse or rat placental tissue (12-18-day gestation) were incubated with C3H]leucine and the biosynthesis of placental CaBP was quantified by an immunoprecipitation method using rabbit antiserum to rat intestinal CaBP. Sodium dodecyl sulfate gel electrophoresis of the radioactive immune complex revealed a single 3Hlabeled peak corresponding to the molecular weight of rat and mouse CaBP (10,050). The amount of CaBP synthesized by mouse placental tissue was dependent upon gestational age of the placenta and reflected the in vivo changes in placental CaBP content observed during gestation. These data indicate that CaBP is synthesized by placenta and provide an in vitro model for studying the developmental control of placental CaBP synthesis.