Identification of whey acidic protein (WAP) in dog milk

Whey acidic protein (WAP) has been identified as a major whey protein in milk of a wide range of species and reportedly plays important roles in regulating the proliferation of mammary epithelial cells. However, in some species including humans, WAP is not synthesized in the mammary gland. The presence of WAP in carnivore species has not been reported. We searched the National Center for Biotechnology Information (NCBI) database for the dog WAP gene and tried biochemically to identify WAP in dog milk. The nucleotide sequence of the examined dog genomic DNA was completely identical to that in the NCBI database and showed that the dog WAP gene, like other known functional WAP genes, has four exons. Biochemical analysis of milk protein by reverse-phase HPLC and Western blotting demonstrated the presence of WAP in dog milk.