Biochemical characterization of mouse vitamin D-dependent calcium-binding protein. Evidence for its presence in embryonic life

Abstract

Immunochemical and biochemical properties of the vitamin D-dependent Ca2+-binding protein (CaBP) from rat and mouse intestine were compared. The 2 intestinal CaBP species were extensively purified by gel filtration and successive anion-exchange chromatographies. Both had a similar MW of 9000. Their pI [negative log of ionization constant] values differed markedly, being 8.0 and 4.9 in rat and mouse CaBP, respectively. Accordingly, mouse CaBP displayed more anodal migration in electrophoresis under non-denaturing conditions. Both mouse and rat CaBP only exhibited partial immunochemical similarities, but their amino acid compositions were very similar. Chromatofocusing was also found to be a good method of detecting Ca2+-dependent changes in their pI. A sensitive radioimmunoassay for mouse CaBP was developed, which enabled detection of substantial amounts of CaBP in uterus, yolk sac and chorio-allantoic placenta. During normal mouse gestation, CaBP appeared on day 12 in the chorio-allantoic placenta but was already present on day 9 in the yolk sac, where its level rose sharply between days 9.5 and 10. CaBP may be considered as a new marker for mouse yolk sac differentiation.