Isolation of Two Forms of Activated Cls, a Subcomponent of the First Component of Rabbit Complement

Abstract

Two forms of activated Cls, a subcomponent of the first component of complement, were present in preparations of C$s¯$ specifically purified from rabbit serum by affinity chromatography on IgG-Sepharose 6B and were separated by DEAE-cellulose chromatography in the presence of EDTA. These two activated Cls, designated Cl$s¯$(I) and Cl$s¯$(II), were indistinguishable with regard to hemolytic activity as well as Cl$s¯$ esterase activity, though they had different molecular weights. Cl$s¯$(I) had a molecular weight of 106,000, consisting of H and L chains connected by disulfide bonds; the molecular weights of the chains were 70,000 and 36,000, respectively. On the other hand, Cl$s¯$(II), with a molecular weight of 72,000, consisted of two chains each with a molecular weight of about 37,000, which were also connected by disulfide bonds. These results suggest that, in the case of rabbit Cls, the primary product of activation with Cl$r¯$, Cl$s¯$(I), may be susceptible to further cleavage of its H chain without any loss of Cl$s¯$ activity, resulting in the formation of Cl$s¯$(II), though the active principle responsible for this conversion remains to be elucidated.