Amino acid sequence of rat .alpha.-lactalbumin: a unique .alpha.-lactalbumin

The amino acid sequence of rat alpha-lactalbumin has been determined. Unlike other alpha-lactalbumins which contain 122 or 123 amino acids, rat alpha-lactalbumin is unique in that it contains 140 amino acids. The extra amino acids are a 17 amino acid extension at the carboxyl terminus. The amino acid sequence of this extension is Gly124-Ala-Pro-Ala-Leu-Val-Val130-Pro-Ala-Leu-Asp-Gly135-Glu-Thr-Pro-Val-Pro140 . The extension is proline rich, which may contribute to the anomalous structural properties of rat alpha-lactalbumin. The amino acid sequence from residues 1 to 123 is similar to that of other alpha-lactalbumins. One possible explanation for the 17 amino acid extension is a mutation at the termination codon.