The E variant of bovine β-casein differs from the reference βA2 variant by the substitution 36 Glu (βA2) → Lys (βE). Seryl residue 35 is phosphorylated in βE as in βA2. The variant βE can be compared to the variant βC which also differs from βA2 by a Glu → Lys substitution. However, this substitution then affects the position 37, and, in this case, the seryl residue 35 is not phosphorylated. These observations tend to support the existence of the phosphorylation code of bovine caseins as postulated by Mercier et al. [1].
