Abstract
The development of C3-cleaving and indirect lysis activity in human serum after the introduction of cobra venom factor (CoVF) was associated with an increase in both the apparent molecular weight and the positive charge of CoVF. After decay at 37°C of these CoVF-induced activities, the CoVF reverted to its native state as assessed by these two physical parameters. No functional differences between native CoVF and CoVF reisolated from decayed CoVF-serum mixtures existed with respect to the factors required for indirect lysis (Factors B, D, and E) and C3 destruction (Factors B and D). In decayed CoVF-serum mixtures, properdin Factor B was in its immunoelectrophoretically converted form, and the addition of fresh Factor B restored full indirect lysis activity. Mixtures of CoVF, Factor D, and Factor B in molar excess of CoVF exhibited no loss of CoVF-dependent activity unless the excess Factor B had been utilized or prevented from recycling with CoVF and Factor D. The behavior of Factor B during the formation and decay of the CoVF-dependent, C3-cleaving enzyme was similar to that of C2 in its interactions with C1̄ and C4.
