title: Formation of angiotensin II by tonin-inhibitor complex.
abstract: Enzymatic activity of tonin-alpha 1-macroglobulin complex was studied in vitro and in vivo, using an immunoimmobilization technique. Tonin-alpha 1-macroglobulin complex, which was immunologically immobilized by anti-alpha 1-macroglobulin antibody covalently coupled to agarose gels, could quantitatively hydrolyze angiotensin I and synthetic tridecapeptide renin substrate to form angiotensin II. However, the solid-phase antibody-bound tonin-alpha 1-macroglobulin complex could not hydrolyze the plasma protein renin substrate. Phenylmethylsulfonyl fluoride, a serine protease inhibitor, inhibited both free tonin and the solid-phase antibody-bound tonin-alpha 1-macroglobulin complex. The hydrolytic activity of the solid-phase antibody-bound tonin-alpha 1-macroglobulin complex against angiotensin I was not inhibited by soybean trypsin inhibitor (molecular weight, 23,000), a potent inhibitor of free tonin. Taken together, these results suggest that tonin bound to alpha 1-macroglobulin keeps the active site intact and that inhibition of the enzyme activity is due to a steric hindrance. When 500 microliter of tonin was administered intravenously to rats, the immunoimmobilization method was used to show that the tonin-alpha 1-macroglobulin complex in the plasma formed angiotensin II. Thus, the tonin-alpha 1-macroglobulin complex in the plasma may be linked to some forms of hypertension through angiotensin II formation.
mesh_terms: D000803:Angiotensin I / Q000378:metabolism*; D000804:Angiotensin II / Q000096:biosynthesis*; D000818:Animals; D006207:Half-Life; D006868:Hydrolysis; D007703:Peptidyl-Dipeptidase A / Q000097:blood / Q000378:metabolism; D011480:Protease Inhibitors / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D000511:alpha-Macroglobulins / Q000494:pharmacology*
chemical_list: D011480:Protease Inhibitors; D000511:alpha-Macroglobulins; D000804:Angiotensin II; D000803:Angiotensin I; D007703:Peptidyl-Dipeptidase A