Important role in the capacity of milk to transport calcium phosphate. Mammary gland specific. Secreted in milk. Allele A, with 11 phosphate groups. The measured range is 16-214. Allele A, with 11 phosphate groups. The measured range is 16-206. Allele C, with 10 phosphate groups. The measured range is 16-206. Allele C, with 10 phosphate groups. The measured range is 16-206. Allele D, with 6 phosphate groups. The measured range is 16-214. Allele D, with 6 phosphate groups. The measured range is 16-214. At least four alleles are known. The sequence shown is that of allele A. The frequency of variant Thr-209 is 0.263, 0.122 and 0.191 in Italian breeds Comisana, Sarda and Sopravissana, respectively. Belongs to the alpha-casein family.