Sulphated proteins secreted by rat mammary epithelial cells.

The main sulphated proteins secreted by rat mammary gland tissue have Mr of approximately 32 000, 27 000 and 25 000 Da. In addition, there are high Mr components which have a diffuse electrophoretic mobility (Mr > 200 000) and most likely corresponded to proteoglycans. The sulphate groups in the proteins with discrete Mr are most likely all linked to carbohydrates. These sulphated molecules were partially purified and identified to isoforms of rat alpha-lactalbumin for the 25-27 kDa bands and to kappa-casein for the 32 kDa band. This pattern of protein sulphation is, as far as we know, quite specific to rat mammary epithelial cells.