Fig. 3. Human platelet osteonectin (H.OSN) contains 1% fibronectin while bovine bone osteonectin (B.OSN) does not contain fibronectin. Serial diluted fibronectin (FN), 500 ng of H.OSN, B.OSN and B.OSN with 3.3 ng FN, was subjected to electrophoresis on 4–12% SDS-PAGE and analyzed by immunoblotting with anti-FN antibody. The amount of osteonectin (500 ng) corresponds to the amount of human platelet osteonectin that promotes cell adhesion. B.OSN was `spiked' with FN as a control. The amount of FN in the H.OSN was quantitated as described and determined to be 5.9 ng, approximately 1% of the H.OSN. This is a representative experiment from three separate experiments.