Biochemical evidence for the presence of two vitamin D-dependent calcium-binding proteins in mouse kidney.

Mouse kidney, a vitamin D target organ, was investigated for the presence of vitamin D-dependent calcium-binding proteins (CaBP). Mouse kidney cytosol was fractionated by several biochemical methods including gel filtration chromatography, gel permeation high performance liquid chromatography, and chromatofocusing. Mouse kidney was found to possess two CaBPs which completely differed biochemically and exhibited no cross-immunoreactivity. One had a molecular weight of 25,000 and a pI of 5.9. The other, with a molecular weight of 10,000 and a pI of 4.9, was biochemically identical with mouse duodenal 10,000 CaBP. In addition, mouse renal and duodenal 10,000 CaBPs were immunologically identical. Moreover, the 10,000 CaBP was the predominant CaBP in mouse kidney since the latter contained about twice as much 10,000 CaBP as 25,000 CaBP (in mol/mg of renal cytosolic protein). In vitro incorporation of [3H]leucine into renal 10,000 CaBP demonstrated that it is synthesized in situ by mouse kidney. Renal 10,000 CaBP was already present during fetal life, and reached its adult level during the first week after birth. The vitamin D dependency of both mouse renal 10,000 and 25,000 CaBPs was assessed by their decrease in vitamin D-deficient mice and subsequent rise after 1,25-dihydroxyvitamin D3 injection. The concomitant presence of substantial amounts of two vitamin D-dependent CaBPs in mouse kidney is peculiar to this organ, which might consequently provide a unique model for studying the hormonal expressions of 1,25-dihydroxyvitamin D3.