Polypeptide having factor Xa inhibitory activity

The present invention provides an antibody which specifically reacts with an epitope of a polypeptide comprising the amino acid sequence X-Y-CYS GLN GLU GLU GLU CYS PRO ASP PRO TYR LEU CYS SER PRO VAL THR ASN ARG CYS GLU CYS THR PRO VAL LEU CYS ARG MET TYR CYS LYS PHE TRP ALA LYS ASP GLU LYS GLY CYS GLU ILE CYS LYS CYS GLU GLU LEU CYS GLN ASN GLN ASN CYS THR LYS ASP MET LEU CYS SER SER VAL THR ASN ARG CYS ASP CYS GLN ASP PHE LYS CYS PRO GLN SER TYR CYS-Z (SEQ. ID NO. 1) wherein X is MET or absent; Y is 0-28 amino acids of the sequence LYS MET CYS TRP ASN LYS GLY CYS PRO CYS GLY GLN ARG CYS ASN LEU HIS ARG ASN GLU CYS GLU VAL ILE ALA GLU ASN ILE GLU, (SEQ. ID NO. 2) with the proviso that if part of the sequence is present, it is a carboxy-terminal part of the sequence including the carboxy-terminal GLU and wherein Val may be preceded by Gly; and Z is absent or all or a part of the sequence Pro110-Lys156 shown in FIG. 7 (SEQ. ID NO. 24), with the proviso that if part of the sequence is present, it is the amino part of the sequence. The present invention also provides a monoclonal antibody as described above.