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The primary structure of ovine beta caseins


, : The primary structure of ovine beta caseins. European Journal of Biochemistry 99(2): 285-298

Ovine whole casein contains 2 multiphosphorylated .beta.-casein components designated as .beta.1 and .beta.2-caseins. The complete sequence of .beta.1-casein and the partial sequence of .beta.2-casein were determined from the intact proteins and from the peptides isolated from CNBr and tryptic digests. The ovine .beta.1 and .beta.2-caseins have the same polypeptide chain and appear to differ only in that they contain 6 and 5 phosphates, respectively. The amino acid composition of ovine .beta.1-casein can be written as: Asp4, Asn4, Thr10, ThrP1, Ser9, SerP5, Glu19, Gln21, Pro34, Gly5, Ala4, Val21, Met6, Ile9, Leu22, Tyr3, Phe9, Trp1, Lys12, His5, Arg3. Compared to bovine .beta.-casein A2, which is made up of 209 residues, ovine .beta.1-casein has a deletion of 2 residues (either Pro-179-Try-180 or Tyr-180-Pro-181) and 20 largely conservative amino acid substitutions. Although 20% of the substitutions involve proline residues, the proline contents of ovine .beta.1 and bovine .beta.A2-caseins are very similar, around 16%. The average hydrophobicity, calculated according to Bigelow, is 5.51 kJ/residue, which is similar to that calculated for bovine .beta.-casein A2. The cluster of 4 phosphorylated serine residues and the highly charged nature of the amino terminal region observed for bovine .beta.-casein are conserved in the ovine .beta.-caseins. The substitution from Ile-12 (bovine) to Thr-12 (ovine) results in a new phosphorylation site, according to the phosphorylation code proposed for caseins. This site is only partially phosphorylated hence the occurrence of both .beta.1 and .beta.2-caseins in ovine milk.

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Related references

Richardson, B.C.; Mercier, J.C., 1979: The primary structure of the ovine beta-caseins. Ovine whole casein contains 2 multiphosphorylated beta-casein components designated as beta 1 and beta 2-caseins. The complete sequence of beta 1-casein and the partial sequence of beta 2-casein have been determined from cyanogen bromide and trypt...

Richardson, B.C.; Mercier, J.C.; Ribadeau Dumas, B., 1978: The primary structure of the ovine beta -caseins. Comparison of the primary structure of (i) ovine beta 1-casein with (ii) bovine beta -casein A2 showed that (i) has a deletion of 2 residues and 20 conservative amino acid substitutions. Although 20% of the substitutions involve proline residues,...

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