Matrix protein profiles in calf bone development.

The major noncollagenous proteins (NCP) of the mineralized extracellular matrix of bovine bone were present from early fetal life through adulthood. The alpha 2-HS-glycoprotein was the dominant bone NCP at 2 months in utero and then diminished with advancing fetal age. Osteocalcin levels were quite low in early fetal bone, became elevated near term, reached a maximum shortly after birth, and dropped again in adult bone. Osteonectin levels were relatively constant at all stages of bone development, but somewhat lower values were seen in woven bone than in lamellar bone matrix. For a given fetus, NCP profiles were identical in both flat and long bones. The 24,000 dalton phosphoprotein was significantly elevated in fetal secondary spongiosa, bony areas known to be undergoing extensive resorption. Adult bone matrix contained greater quantities of lower and intermediate molecular weight NCPs compared to actively forming fetal bone.