Differences between individuals in high-molecular weight glycoproteins from mammary epithelia of several species.

Milk fat globules are secreted by envelopment in plasma membrane of the lactating cell. SDS-gel electrophoresis of proteins from this membrane has revealed differences between milk donors in two mucin-like glycoproteins. One of these glycoproteins resolves in 3% acrylamide stacking gel and the other in 4% running gel. The proteins vary in number of bands (one or two) and band mobilities. This polymorphism arises, at least in part, from expression of hypervariable genes. In this study, gel electrophoretic evidence of similar polymorphism in glycoproteins from cow, chimpanzee, horse and human milks is presented. In distinction to the other species, the cow expressed only one of these proteins which was detected in the running gel at Mr 180,000 to 200,000. The electrophoresis pattern for this protein from six cows was highly varied with respect to number (one or two) and position of bands. Peanut agglutinin, wheat germ agglutinin and concanavalin A all were bound specifically by bands of the bovine glycoprotein. Binding of concanavalin A distinguishes the bovine protein from the two human glycoproteins. Further studies of species differences should help shed light on the evolution of these unique glycoproteins and their possible functions in mother and young.