C5 Activation by Enzymes of the Alternative Pathway of the Complement System. The Reaction of a C3 Cleaving Cobra Factor-B-Enzyme (VF-B̄) with Guinea Pig C5

Abstract

The Cobra venom factor (VF) is able to form a complex with Factor B of the alternative pathway of the complement system, which then in the presence of Factor D or trypsin is activated to the C3 cleaving enzyme VF-B̄. C3 activation caused by the enzyme in serum is accompanied by an activation of the components C5 to C9. The reaction mechanism which controls the activation of C5 has been unclear until now. We have generated the VF-B̄ enzyme in three different ways; I, with VF in serum followed by purification of the enzyme; II, with VF, B and D and subsequent Sephadex G-200 gelfiltration; and III, with VF, B and trypsin and subsequent Sephadex G-200 gelfiltration. The activity of these three enzymes was tested against purified guinea pig C3, C5, and a mixture of C3 and C5. The following observations were made: All three enzymes induce fast C3 activation with accumulation of C3b and C3a; C3b is detected afterward on the enzymes antigenically, on enzyme I immediately after the generation and purification procedure.