We identified a novel metalloprotease, which could be responsible for cleaving the Tyr842-Met843 peptide bond of von Willebrand factor (vWF). This metalloprotease was purified from Cohn Fraction-I precipitate of human pooled plasma by the combination of gel filtration, DEAE chromatography, and preparative polyacrylamide gel electrophoresis in the presence of SDS. The NH₂-terminal amino acid sequence of the isolated protein was: AAGGILHLELLVAVGPDVFQAHQEDTRRY. Based on this sequence, we searched human genomic and EST databases, and identified compatible nucleotide sequences. These results suggested that this protein is a novel metalloprotease, a member of the family of a disintegrin and metalloprotease with thrombospondin type-1 motifs (ADAMTS), and its genomic DNA was mapped to human chromosome 9q34. Multi-ple human tissue northern blotting analysis indicated that the mRNA encoding this protease spanned approximately 5 kilobases and was uniquely expressed in the liver. Furthermore, we determined the cDNA sequence encoding this protease, and found that this protease was comprised of a signal peptide, a proregion followed by the putative furin cleavage site, a reprolysin-type zinc-metalloprotease domain, a disintegrin-like domain, a thrombospondin type-1 (TSP1) motif, a cysteine-rich region, a spacer domain, and COOH-terminal TSP1 motif repeats.