Polyacrylamide Gel Electrophoresis (PAGE) of Reduced and Dissociated C3 and C5: Studies of the Polypeptide Chain (PPC) Subunits and Their Modifications by Trypsin (TRY) and C42-423.

Our previous PAGE studies (according to Weber and Osborn) revealed an α and a β PPC of C5 of the approximate m.w. of 120,000 and 80,000, respectively. Our present studies show a similar structure of human C3, with an α and a β PPC of approximately 110,000 and 70,000 m.w. respectively. Furthermore, the effects of TRY and of - on C3 and C5 were explored by immunoelectrophoresis (IEP) and by PAGE. C3b (TRY) and C3b () were both faster than C3 and indistinguishable by IEP. C5b (TRY) was distinctly faster than C5b () which was, however, only slightly faster than C5 by IEP. PAGE analysis indicated that the modifications observed by IEP were all related to degradations of the α PPC:s of C3 and C5: conversion of C3 to C3b (TRY) or C3b () coincided with a reduction of the m.w. of the α PPC of C3 by approximately 7000 to 8000; conversion of C5 to C5b (TRY) coincided with the reduction of the α PPC of C5 by approximately 18,000, whereas conversion of C5 to C5b () coincided with a reduction by less than 18,000. The changes occurred in the absence of detectable modification of the β PPC:s of C3 and C5. Our data suggest that the α PPC:s of C3 and C5 are the likely origins of C3a and C5a, respectively. (Supported by United States Public Health Service Grant AM13515.)