A human lung mast cell chymotrypsin-like enzyme. Identification and partial characterization

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• Mast cells are key immune cells involved in allergic reactions and inflammation.
• The enzymatic activity within mast cells, particularly their secretory granules, is crucial for their function.

Purpose of the Study:

• To investigate the presence and characteristics of chymotryptic activity in human lung mast cells.
• To determine if this chymotryptic activity is associated with mast cell secretory granules and allergic responses.

Main Methods:

• High-performance liquid chromatography (HPLC) assay to detect chymotryptic cleavage of angiotensin I.
• Purification of human lung mast cells using enzymatic dispersion, countercurrent elutriation, and Percoll gradient centrifugation.
• Analysis of mast cell lysates and IgE-challenged cells, including dose-response experiments and enzyme inhibition studies.

Main Results:

• Chymotryptic activity, converting angiotensin I to angiotensin II, was detected in human lung mast cell preparations.
• A significant correlation was observed between histamine release and angiotensin I-converting activity, indicating the enzyme's presence in secretory granules.
• The enzyme exhibited a pH optimum of 7.5-9.5, was inhibited by phenylmethylsulfonylfluoride, and had an approximate molecular weight of 30-35,000 Da.

Conclusions:

• Human lung mast cells possess a chymotrypsin-like enzyme with angiotensin II-converting activity.
• This enzyme is a constituent of mast cell secretory granules and is distinct from tryptase and leukocyte cathepsin G.
• The enzyme's kinetic properties suggest a potential physiologic role in angiotensin II generation.