Abstract
A basic polypeptide that stimulates DNA synthesis and cell division in confluent populations of mouse Balb/c-3T3 cells has been isolated from whole human serum, and has been separated from the heterogenous group of molecules with insulin-like activity. This highly purified basic polypeptide has a molecular weight of 1.3 x 10(4) and an isoelectric point of 9.7. Approximately 10(7) polypeptide molecules in the growth medium allow the replication of one density-inhibited cell.