Sequencing β-Casein C:Isolation of a Large Fragment After Cleavage of Thioltrifluoroacetylated β-Casein C

A large fragment of β-casein C consisting of residues 26 to 184 was isolated by trypsin cleavage of lysine derivatized protein. The first 26 amino acid residues of the fragment are identical to those of the corresponding region in β-casein A2 with the exception of a lysine/glutamic acid substitution and the absence of phosphorus on a serine residue phosphorylated in β-A2. The apparent absence of γ-casein in milks containing β-casein C is also discussed.