PURIFICATION AND CHARACTERIZATION OF INSULIN-LIKE GROWTH-FACTOR-II (IGF-II) AND AN IGF-II VARIANT FROM HUMAN PLACENTA

In order to purify variant IGF II peptides from human placenta, we hav e developed a purification procedure combining heparin affinity chroma tography and cation-exchange, reversed-phase and size-exclusion HPLC. Two peptides were purified, both having apparent M(r) values of ca. 73 00 Da as evaluated by SDS-PAGE. N-Terminal sequencing revealed IGF II and an IGF II variant in which Ser(29) was replaced by the tetrapeptid e Arg-Leu-Pro-Gly. The final yield of variant IGF II was about eight-f old lower than that of IGF II. Both pure peptides were functionally ac tive as they bound to type I and type II IGF receptors from ovine and human placental membranes, as determined by crosslinking experiments a nd displacement curve studies.