Constituent of ilotropin, which is a partially purified preparation of cellophane wrapping (CW) pancreata. Capable of initiating duct cell proliferation, a prerequisite for islet neogenesis. Expressed only in CW animals pancreas and to a lesser extent in duodenum. In pancreas it is found in acinar cells, but not in islets. Found 1 and 2 days after cellophane wrapping, absent by the 6th day. This period coincides with islet neogenesis. It is uncertain whether Met-1, Met-2 or Met-5 is the initiator.