The Composition, Structure and Origin of Proteose-peptone Component 8F of Bovine Milk

Proteose-peptone component 8F (or ‘8-fast’) has been prepared from bovine milk. Sedimentation equilibrium analysis, polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate and gel filtration in urea-containing buffers all gave molecular weight values between 3300 and 3900. The N-terminal sequence was found to be Arg-Glu- by dansylation and Edman degradation. Hydrazinolysis released lysine from the C-terminus. A mixture of carboxypeptidases A and B showed that the C-terminal sequence was -Thr-(Arg,lle,Asn)-Lys. The phosphate content was 3.8 mol/mol and was completely released by a short alkaline hydrolysis indicating linkage to serine. This and all other aspects of the composition were entirely consistent with the identification of this proteose-peptone as residues 1–28 of the β-casein molecule. This identity was confirmed by a peptide mapping procedure. Thus proteose-peptone component 8F represents the N-terminal fragment when the γ1-caseins are formed by proteolysis of β-casein.