The multimeric structure and disulfide-bonding pattern of bovine kappa-casein.

Bovine kappa-casein was analyzed by SDS/PAGE, MS and amino acid sequence analysis in order to determine its multimeric composition and disulfide-bonding pattern. SDS/PAGE revealed that kappa-casein in the native state can range in size from a monomer to a multimeric structure larger than a decamer. Three types of interchain disulfide linkage, Cys11-Cys11, Cys11-Cys88 and Cys88-Cys88, were all assigned in multimers purified from [14C]carboxymethylated and untreated bulk milk, as well as a milk sample from a kappa-casein-variant-B homozygote Co20. These results indicate that multimerization occurs in a random or at present unpredictable disulfide-bonding pattern regardless of the size of the multimer or the genotype.