Am. J. Respir. Cell Mol. Biol., Vol 12, No. 4, 04 1995, 441-448.
Isolation and properties of an angiotensin II-cleaving peptidase from mesquite pollen
N Matheson, J Schmidt and J Travis
Department of Biochemistry, University of Georgia, Athens 30605, USA.
Biochemical studies of pollen proteins have been focused, primarily, in
investigating their roles as allergens. These molecules, some of which have
enzymatic activity, act as antigens and initiate the production of IgE
antibodies, leading to allergic and/or asthmatic responses. Included in
this mixture of proteins are proteinases which, although they may or may
not be allergenic, could still be involved in airway dysfunction. We have
isolated an arginine-specific endopeptidase to homogeneity from mesquite
(Prosopis velutina) pollen, a known wind- borne allergen, which has a
molecular mass near 84 kDa by NaDodSO4-gel electrophoresis, a pH optimum in
the neutral to alkaline range, and a requirement for Ca2+ for
stabilization. The enzyme is inhibited by diisopropyl fluorophosphate (DFP)
and N-p-tosyl-L-lysine chloromethylketone but not by
N-p-tosyl-L-phenylalanine chloromethylketone, EDTA, or iodoacetamide. It
was also not inhibited by human plasma proteinase inhibitors nor several
other naturally occurring plant and animal inhibitors. Cleavage by the
endopeptidase was primarily on the carboxy-terminal side of arginine
residues in peptides, whereas proteins such as kallikrein and prothrombin
were only activated and/or degraded extremely slowly. Several bioactive
peptides that may be involved in maintaining normal lung function were
readily fragmented, including angiotensin II, a vasoconstrictor, and atrial
natriuretic peptide, a modulator of vascular permeability, both of which
were rapidly cleaved at low enzyme:substrate molar ratios. Thus, the pollen
endopeptidase could be involved in exacerbating the development of asthma
by inactivating bioactive peptides that have ameliorating effects in
maintaining lung airway homeostasis.
