A substance immunologically cross-reactive with insulin (SICRI) was isolated and purified from murine melanoma B16 and myeloid leukemia. 2. Monospecific anti-insulin immunoglobulin G was coupled with CNBr-activated Sepharose 4B to yield an adsorbent. The immunoaffinity column was used to isolate SICRI from tumor tissue. 3. Purified SICRI yielded a single band with mol. wt 158,000 on SDS-PAGE. After non-denaturing conditions SICRI appeared again in one single peak. 4. Affinity purified SICRI was shown to be a potent growth factor for different human and murine transformed and normal cells. 5. Biochemical and biological data provide evidence that SICRI and insulin are two distinct biologically active agents.
