Protein fractions from mouse salivary glands affecting epithelial cells in organ culture.

1. Extracts of male mouse submaxillary gland have been fractionated on G 150 Sephadex and DEAE cellulose.2. A number of the protein fractions obtained appear to cause proliferation of epithelial cells in organ cultures of rat tissues.3. All fractions active in organ culture possess proteolytic enzyme activity.4. The proteolytic enzymes trypsin, pronase and collagenase produce epithelial disorganization in organ culture.5. The organ culture effect is reduced in the presence of proteolytic enzyme inhibitors and abolished by pretreatment of proteins with diisopropylfluorophosphonate.6. The presence of mitotic inhibitors does not reduce the organ culture effect.7. The effect is not associated with an increase in the DNA content of tissue explants.8. No evidence has been found for the existence, in mouse salivary glands, of a specific growth factor acting on epithelial cells.