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_??_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_??_(I) and Cl_??_(II), were indistinguishable with regard to hemolytic activity as well as Cl_??_esterase activity, though they had different molecular weights. Cl_??_(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_??_(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_??_, Cl_??_(I), may be susceptible to further cleavage of its H chain without any loss of Cl_??_activity, resulting in the formation of Cl_??_(II), though the active principle responsible for this conversion remains to be elucidated.