Purification of a basic somatomedin, from human plasma Cohn fraction IV-1, with physicochemical and radioimmunoassay similarity to somatomedin-C and insulin-like growth factor.

A basic somatomedin (SM) was purified from human plasma Cohn fraction IV-1 using an initial acid--ethanol--acetone extraction procedure followed by alternating molecular size or charge protein separation techniques. The final recovery of SM bioactivity was approximately 2% of that present in the starting Cohn fraction. The purified SM has an approximate molecular weight of 7500, pI 8.6, 4000 SM bioactivity units per milligram (as measured by a hypophysectomized rat bioassay) and a parallel approximately equipotent radioimmunoassay dose--response curve to SM-C and insulin-like growth factor-1 (IGF-I). Sodium dodecyl sulfate--polyacrylamide gel electrophoresis of this purified SM revealed a single protein band. The preliminary determination of the amino acid sequence of the N terminus suggested that this SM preparation was over 75% pure and the first five N-terminal amino acids were identical with those of IGF-I.