C4 polymorphism in the dog: molecular heterogeneity of the C4 alpha and C4 gamma subunit chains.

Using an immunoblotting technique and goat antihuman C4, we observed five distinct electrophoretic variants of C4 in a panel of 60 random dogs. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of immunoprecipitated C4 showed that dog C4 is composed of three polypeptide subunit chains (alpha, beta, and gamma) and that structural variability occurs within the alpha- and gamma-chain regions. Two distinct molecular weight forms of both the C4 alpha- (alpha A and alpha B) and C4 gamma- (gamma A and gamma B) chain were detected. The variant forms of C4 alpha and C4 gamma were found in association with particular C4 allotypes.