title: C3 activation by a new factor B-dependent enzyme detected in culture supernatant from guinea-pig peritoneal macrophages.
abstract: Culture supernatants (c.s.) collected from thioglycollate-elicited macrophages were concentrated and incubated with purified C3. In this reaction mixture loss of haemolytic C3 according to classical enzyme kinetics was observed. As revealed by SDS-PAGE, c.s.-catalysed fragmentation of the C3 alpha-chain occurred. The cleavage products were identified by size and function as C3a and C3b. The apparent molecular weight of this C3-activating enzyme in c.s. was approximately 220,000 according to ultracentrifugation studies. This large enzyme showed the following characteristics: it had no activity against C5; it was inhibited by EDTA; Mg2+ was required for its optimal function; its half-life at 37 degrees was approximately 35 min; it was completely inhibited by anti-B IgG. Thus, we were able to detect a C3-activating enzyme in c.s. containing B but differing otherwise from a preformed C3 convertase of the alternative pathway. The exact component composition of this new enzyme is under further investigation.
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D003166:Complement Activating Enzymes / Q000378:metabolism*; D003167:Complement Activation; D003176:Complement C3 / Q000378:metabolism*; D015926:Complement C3a; D003179:Complement C3b / Q000378:metabolism; D003182:Complement C5 / Q000378:metabolism; D011415:Complement Factor B / Q000378:metabolism; D011416:Complement Factor D / Q000378:metabolism; D004492:Edetic Acid / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D006168:Guinea Pigs; D006461:Hemolysis; D007074:Immunoglobulin G / Q000276:immunology; D008264:Macrophages / Q000201:enzymology*; D008274:Magnesium / Q000494:pharmacology; D008970:Molecular Weight
chemical_list: D003176:Complement C3; D003182:Complement C5; D007074:Immunoglobulin G; D015926:Complement C3a; D003179:Complement C3b; D004492:Edetic Acid; D003166:Complement Activating Enzymes; D011416:Complement Factor D; D011415:Complement Factor B; D008274:Magnesium