Effect of dephosphorylation on bovine casein

Bovine whole casein, α- and β-casein were dephosphorylated by potato acid phosphatase (EC 3.1.3.2); the extents of dephosphorylation were as follows: whole casein 71.6%, α-casein 89.2% and β-casein 73.7%. SDS-PAGE, urea-PAGE, RP-HPLC and ESI-MS demonstrated effects of dephosphorylation on the caseins; α- and β-casein showed both proteolysis and dephosphorylation while whole casein showed only dephosphorylation. Urea-PAGE and ESI-MS confirmed the identities of the individual fractions. ESI-MS established (a) the MW for α- and β-casein as 23 612 and 24 017 kDa, respectively, (b) random removal of 1, 2, 4, 6, 7 and 8 phosphate groups during dephosphorylation of α-casein, (c) random removal of 1, 2, 3, 4 and 5 phosphate groups during dephosphorylation of β-casein and (d) limited dephosphorylation of both α-casein (1 and 2 phosphates) and β-casein (1 phosphate) in the absence of the phosphatase.