Occurrence of three novel αs1-casein variants in goat milk

In order to evaluate the quality of caprine milk from Italian breeds, individual samples were submitted to detailed casein analysis and attention focused mainly on alpha(s1)-casein. Three novel variants were detected using gel electrophoretic techniques. The primary structure of three HPLC-purified alpha(s1)-casein variants was determined with the aid of spectrometry techniques, for example electrospray mass spectrometry on intact protein, and fast atom bombardment in combination with Edman degradation on peptides to map the protein. Taking into account the present state of knowledge on alpha(s1)-caprine polymorphism, the novel variants were labelled with the symbols H, I, and L. The negative charge of the H variant was similar to that exhibited by the a variant, whereas the iso-electric point (pI) was lower, owing to the amino acid substitution Arg(1) (A) --> Lys(1) (H) on the N-terminal residue. Taking into account the alpha(s1)-casein level, the H variant was classified as a hard allele. Variant I presented similar values for pi and molecular mass, whereas the amino acid sequence was the same as that of alpha(s1)-casein A, the only difference being that the I variant showed about half the amount of casein than the A variant. The L variant exhibited the highest anodic mobility among the alpha(s1)-casein variants detected in caprine breeds up to now, a PI similar to that of the B-2 variant, a single amino acid substitution Arg(90) (B-2) --> His(90) (L), and a alpha(s1)-casein expression similar to that of the "hard" alleles.