Purification of bovine somatomedin.

A procedure for the purification of bovine somatomedin (SM⁴) is presented. The purification scheme utilizes ultrafiltration through membranes of nominal mol. wt. cutoffs, molecular sieve chromatography and finally iso-electric focusing. Two peaks of SM activity, measured by the $\text{in vitro}$ stimulation of ³⁵S-Na₂SO₄ and ³H-thymidine uptake by costal cartilage, were present after focusing; an acidic component having a pI of 6.0 – 6.7 and a basic component having a pI in the range of 7.8 – 8.3. The acidic component comprised 2% of the initial activity and was 120,000-fold purified: the basic component comprised 10% of the initial activity and was 350,000-fold purified relative to the starting material. These components are similar in molecular size and pI to SM-A and SM-C isolated from human plasma.