Structural and immunological differences between human platelet and endothelial thrombospondins

The structural and immunological properties of human thrombospondins isolated from platelets and from endothelial cells were compared. Both thrombospondins were digested with either trypsin or thermolysin, in the presence or absence of calcium, then injected onto a Superose 12 gel filtration column. The isolated thermolysin-generated fragments of thrombospondins were identified by radioimmunoassays using either different monoclonal antibodies or a polyclonal antibody directed against platelet thrombospondin. The results show that platelet and endothelial thrombospondins are both partially protected from trypsin digestion in the presence of calcium but have different trypsin and thermolysin fragmentation patterns. The thermolysin-generated fragments from platelet and endothelial thrombospondins are recognized differently by a monoclonal antibody whereas all of them are identified by a polyclonal antibody.