Purification and substrate specificity of an angiotensin converting elastase-2 from the rat mesenteric arterial bed perfusate.

Abstract

A soluble angiotensin (Ang) II-generating enzyme has been purified to homogeneity from the rat mesenteric arterial bed(MAB) perfusate by a combination of gel filtration and affinity chromatographies. The enzyme is a glycoprotein of 28.5 kDa(SDS-PAGE), whose N-terminal sequence is identical with that of the rat pancreatic elastase-2 ; therefore the enzyme willhenceforth be referred to as rat MAB elastase-2. When Ang I was used as the substrate, the enzyme specifically released AngII and the dipeptide His-Leu (Km=36WM;Kcat= 1530 min31). The catalytic efficiency (Kcat/Km= 42.5 min31WM31) of thisreaction was comparable to those of other known Ang I-converting enzymes. The proteolytic specificity of the purifiedenzyme toward mellitin, oxidized insulin B chain, somatostatin-14 and renin substrate tetradecapeptide suggested that theenzyme-substrate interaction was defined by an extended substrate binding site, typical of elastases-2 of pancreatic origin. According to the sensitivity of the rat MAB elastase-2 to various inhibitors this enzyme could be described as a member ofthe chymostatin-sensitive group of Ang II-forming serine proteases. The localization and biochemical properties of thisenzyme suggest that it might play a role in the regional control of vascular tonus.