Alpha-lactalbumin as a lysosomal enzyme-releasing factor.

In the early stage of mammary gland involution, biochemically detectable lysosomal damage occurs. The mechanism(s) underlying this damage is not well understood. We found that alpha-lactalbumin from mouse milk induced the release of enzymes from the lysosomes of mouse mammary epithelial cells in vitro, and this induction also occurred with bovine alpha-lactalbumin. This enzyme release was accelerated by the addition of whey proteins with a molecular weight of 50 000 to 60 000. We also found that the lysosomal membrane of mammary epithelial cells had a strong affinity for alpha-lactalbumin.