Generation of the classical pathway C3 convertase (EAC4b2a) by proteolytic enzymes.
The formation of EAC 4b2a is a two step reaction: first, the temperature- and time-independent binding of C2 to EAC4b2a resulting in EAC4b2 , secondly, the enzymatically triggered conversion of EAC4b2 to EAC4b2a . In the classical cascade of complement activation, the generation of C3 convertase activity is triggered by the C1 esterase, C1-s, which is part of C-1. Evidence is presented that the enzymes trypsin, chymotrypsin, plasmin, and pronase are also able to activate EAC4b2 to EAC4b2a . Kinetic studies showed that the formation of C3 convertase by these enzymes was dependent on concentration, temperature, and time. The optimal conditions were found as follows: trypsin, 2 micrograms/ml (final conc.) for 8 min at 23 degrees C; chymotrypsin 165 micrograms/ml for 18 min at 23 degrees C; plasmin 0.8 units/ml for 15 min at 23 degrees C; pronase 1.25 microgram/ml for 15 min at 23 degrees C. Even under optimal (tmax) conditions the number of generated EAC4b2a differed from enzyme to enzyme: trypsin (= 100%), pronase (58.3%), chymotrypsin (47.9%), and plasmin (12.9%). The enzymes were also able to generate C3 convertase activity from C2 which was adsorbed to EAC1i4b , a C1 inactivator treated and therefore hemolytically inactive intermediate ( EAC1i4b2 ). These findings underline the biological importance of C1 esterase replacing enzymes.
D000818:Animals; D003166:Complement Activating Enzymes / Q000096:biosynthesis*; D003174:Complement C1 Inactivator Proteins / Q000494:pharmacology; D003173:Complement C1s / Q000378:metabolism; D003175:Complement C2 / Q000378:metabolism; D050577:Complement C3-C5 Convertases / Q000096:biosynthesis*; D003181:Complement C4 / Q000378:metabolism; D015935:Complement C4b; D003171:Complement Pathway, Classical; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007700:Kinetics; D010447:Peptide Hydrolases / Q000378:metabolism*; D012756:Sheep; D013696:Temperature
D003174:Complement C1 Inactivator Proteins; D003175:Complement C2; D003181:Complement C4; D015935:Complement C4b; D003166:Complement Activating Enzymes; D010447:Peptide Hydrolases; D050577:Complement C3-C5 Convertases; D003173:Complement C1s