Abstract
Human milk contains a mitogenic factor that stimulates DNA synthesis and cell division in mouse and human fibroblasts in vitro. Milk at a concentration of 1% (vol/vol) is as active in stimulating DNA synthesis as is 5% (vol/vol) human serum and 10% (vol/vol) calf serum. The mitogenic activity of human milk is destroyed by incubation with trypsin and chymotrypsin. However, neither urea, guanidine hydrochloride, dithiothreitol, nor exposure to pH 1 will inactivate the milk-derived growth factor. Gel filtration and isoelectric focusing indicate that the mitogenic activity of human milk has a MW between 14,000-18,000 and an isoelectric point between 4.4-4.7.