An Improved Method for the Purification of Human Insulin-Like Growth Factors I and II*

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Abstract
Insulin-like growth factors (IGFs) I and II have been purified from Cohn fraction IV-1 of human plasma. After acid-ethanol extraction, the consecutive use of conventional gel filtration and reverse phase liquid chromatography has permitted the rapid isolation of these polypeptides. Purification was monitored by the use of specific RIAs. In both chromatography systems, separation was optimized by performing on the same stationary phase but successively with mobile phases of different pH or different solute selectivity. The two polypeptides were shown to be pure by their unique amino acid composition, particularly by the absence of specific amino acids (histidine, tryptophan, and methionine), and their unique amino-terminal sequences. In addition, the lack of cross-contamination of the two growth factors with each other was established by the unique isoelectric focusing patterns of IGF-I at pI 8.25 and IGF-II at pI 6.5. From 900 g Cohn fraction IV-1, which is equivalent to 66 liters human plasma, approximately 100 .mu.g of each IGF can be obtained by our procedure, which can easily be carried out in a clinical research laboratory.