Purified proenzyme C1r. Some characteristics of its activation and subsequent proteolytic cleavage.

摘要: Abstract 1. Upon incubation for 1 h at 37°C, proenzymic C1r was activated by a proteolytic cleavage comparable to that observed in vivo; after reduction and alkylation, two fragments of apparent molecular weights 57 000 35 were evident on sodium dodecyl sulphate (SDS)-polyacrylamide gel electrophoresis. The activation kinetics slightly sigmoidal nearly independent concentration. They characterized marked thermal dependence (activation energy = 45 kcal/mol ). reaction inhibited calcium p- nitrophenyl -p′- guanidinobenzoate , but poorly sensitive di-isopropyl phosphorofluoridate. the rate pH unusual; it decreased progressively acid range (pH 4.5–6.5) which coincides with dissociation C1r-C1r dimer. Above 6.5, increased showed no clear maximum. These results are consistent an intramolecular autocatalytic mechanism involving prosite each subunit 2. During 5 period C r underwent cleavages led successive removal fragments, α (35 000) β (7 000–11 from subunit, leaving dimeric molecule reduced size ( M 110 000; s 20, w 6.1 S process concentration optimum 8.5–9.0, high (36.8 kcal/mol). Calcium also phosphorofluoridate benzamidine inhibitors this reaction. product, II, retained original antigenic properties functional active site, lost capacity bind r. proteolysis mediated site r-C