Biosynthesis of O‐phosphoserine‐containing phosphoproteins by isolated bone cells of mouse calvaria

Five groups of isolated bone cells from mouse calvaria were incubated with [3H]serine and the presence and amount of O-[3H]phosphoserine used as an indication of phosphoprotein synthesis. Cells in the osteoblastic fraction were the most active in synthesizing phosphoproteins, and unlike the other cell groups, released most of the phosphoproteins into the tissue culture medium. When subjected to molecular sieving and ion-exchange chromatography, the phosphoproteins synthesized by the bone cells of the osteoblastic group behaved like the phosphoproteins extracted from mouse calvaria by EDTA.