Mouse C3b/C4b inactivator: purification and properties.
Mouse C3b/C4b inactivator (C3b/C4bINA) was purified approximately 400 times from mouse serum. It is a beta-globulin and consists of 2 disulfide bonded chains of m.w. 60,000 and 35,000. Under nonreducing conditions, its m.w. is 95,000. It cleaves the alpha'-chain of cell-bound C4b into 3 fragments: alpha 2, alpha 3, alpha 4. The alpha 2 fragments remain bound to the cell surface (C4d), and the rest of the molecule (C4c) is released into the fluid phase. In fluid phase, C3b/C4bINA cleaves the alpha'-chain of C4b in a similar manner but only in the presence of mouse or human C4-binding protein (C4-bp). Mouse C4-bp and human C3b/C4bINA do not cleave human C4b, although mouse C4-bp binds to human C4b. This incompatibility suggests that C4-bp and C3b/C4bINA must interact to cleave fluid phase C4b. Mouse C3b/C4bINA also cleaves the alpha'-chain of human C3b in solution into 2 fragments in the presence of human beta 1H. Therefore, it is likely that mouse and human C3b/C4bINA are homologous proteins. A monospecific antiserum to mouse C3b/C4bINA has been prepared in rabbits. By crossed immunoelectrophoresis, this antiserum detects, in addition to the protein described above, a fast beta-globulin with a m.w. of approximately 200,000 and antigenically identical to C3b/C4bINA but enzymatically inactive. This protein could represent a precursor of C3b/C4bINA.
D000818:Animals; D055598:Chemical Phenomena; D002621:Chemistry; D003180:Complement C3b Inactivator Proteins / Q000276:immunology / Q000302:isolation & purification*; D003181:Complement C4 / Q000302:isolation & purification*; D003429:Cross Reactions; D006168:Guinea Pigs; D006801:Humans; D005779:Immunodiffusion; D007123:Immunoelectrophoresis, Two-Dimensional; D008297:Male; D051379:Mice; D008806:Mice, Inbred AKR; D008970:Molecular Weight; D011817:Rabbits
D003180:Complement C3b Inactivator Proteins; D003181:Complement C4