The ability to convert angiotensin (Ang) I to Ang 11 was compared between human alpha-chymase and two mouse beta-chymases, mouse mast cell protease (mMCP)-1 and mMCP-4. Human chymase hydrolyzed Ang I to produce Ang 11 without further degradation. mMCP-1 similarly generated Ang 11 from Ang I in a time-dependent manner and the formation of the fragment other than Ang 11 was marginal. In contrast, mMCP-4 hydrolyzed Ang I at two sites, Tyr(4)-Ile(5) and Phe(8)-His(9), with Ang 11 formation being tentative. Consistently, mMCP-4 but not human chymase hydrolyzed Ang 11 and mMCP-1 showed little hydrolytic activity against Ang II. These data suggest that not only human chymase but also mMCP-1 might possess a physiological role in Ang II formation. Our findings also imply that the Ang-converting activity of chymase may not be related to the categorization of chymase into alpha- or beta-type based on their primary structure. (C) 2003 Elsevier Science (USA). All rights reserved.