This work generated many truncated proteins and Glu(385) to Ala (E-385/A) mutants of the human metalloproteinase and thrombospondin 1 (METH-1 or ADAMTS1) and specific antibodies. METH-I was an active endopeptidase and both the metalloproteinase and the disintegrin/cysteine-rich domains were required for the proteinase activity. A point mutation at the zinc-binding site (E-385/A) abolished the catalytic activity. METH-1 protein function may be modulated through proteolytic cleavage at multiple sites. One 135 kDa species had an NH2-terminal sequence of L(33)GRPSEEDEE. A species at 115 kDa and some other protein bands began with (FVSSHRYV243)-V-236, indicating that METH-1 proenzyme might be activated by a proprotein convertase such as furin by cleaving the R-235-F-236 peptide bond. This cleavage was not an autocatalytic process since the E (385)/A mutants were also processed. Furthermore, a 52 kDa band with an NH2-terminal sequence of L(800)KEPLTIQV resulted from the digestion between the first and the second thrombospondin I-like motifs in the spacer region of the extracellular matrix-binding domains. (C) 2002 Elsevier Science (USA). All rights reserved.