Recent evidence indicates that metalloproteinases and disintegrins, nonenzymatic inhibitors of platelet aggregation, are derived by proteolysis from common precursors. Although proteins and polypeptides with various domain structures have been identified, proteins containing proprotein domains or the complete mature precursors have not yet been isolated. This prompted a closer examination of the putative start codon, signal peptide and the segment upstream of these regions. A critical evaluation of sequence information of these precursors indicates that the putative signal peptide identified in these precursors may be an internal hydrophobic segment within the precursor. There is also evidence to indicate that C-type lectin-related proteins are also derived from these precursors. Thus the available sequence data of the precursors appear to be incomplete.