Neutral protease cleaving the N-terminal propeptide of type III procollagen: partial purification and characterization of the enzyme from smooth muscle cells of bovine aorta

Procollagen type III amino-terminal protease was detected in cultures of smooth muscle cells of fetal calf aorta, and this protease was purified about 400-fold. Only about half of the enzyme activity was consistently attached to concanavalin A-agarose (Con A-agarose). After affinity chromatography on type III pN-collagen-Sepharose, the Con A bound fraction showed only one major band with a molecular weight of about 72000, this value corresponding well with the elution position of enzyme activity in gel filtration. The enzyme did not cleave procollagens type I or type IV, and denatured type III pN-collagen also remained uncleaved. The Km of the enzyme activity for iodo[14C]acetamide-labeled type III pN-collagen was 0.76 microM. Neutral pH and Ca2+ wer required for maximal enzymic activity. The metal chelators ethylenediaminetetraacetic acid and ethylene glycol bis(beta-amino-ethyl ether)-N,N,N',N'-tetraacetic acid inhibited the activity as well as did dithiothreitol, but there was only little if any inhibition by several other proteinase inhibitors tested.