Lactose Synthesis in a Monotreme, the Echidna (Tachyglossus aculeatus): Isolation and Amino Acid Sequence of Echidna α-Lactalbumin

α-Lactalbumin and lysozyme were each isolated from echidna (Tachyglossus aculeatus) milk by gel permeation and ion exchange chromatography. The α-lactalbumin modified the action of echidna milk galactosyltransferase to promote the synthesis of lactose but had very little effect on bovine galactosyltransferase. Echidna α-lactalbumin is a glycosylated protein with an apparent molecular weight of 20,000 (SDS-PAGE) whose concentration in the milk is very low compared with the concentrations of α-lactalbumin in the milk of other species. Its amino acid sequence is more similar to that of another monotreme, the platypus (Ornithorhynchus anatinus), than to the sequences of eutherian or marsupial α-lactalbumins. Echidna milk lysozyme, even at high concentrations, did not promote the synthesis of lactose by either echidna or bovine galactosyltransferase. We conclude that lactose synthesis in the echidna occurs by the same mechanism as that found in the platypus and other mammals.