Vitamin D3-induced calcium binding protein in bone tissue.

As detected by radioimmunoassay with antiserums against chick intestinal calcium binding protein (CaBP), administration of vitamin D3 to rachitic chicks causes a 25- to 100-fold increase in immunoreactive CaBP in chick bone. The bone CaBP has a higher molecular weight (approximately 34,000 daltons) than intestinal CaBP (28,000 daltons), is concentrated principally in the spongiosa and cartilage plate regions of tibia, and responds adaptively to reflect the level of dietary calcium.