Isolation of insulin-like growth Factors I and II from human plasma.

Insulin-like growth factors I and II have been isolated from Cohn fraction IV-1 of human plasma using gel permeation chromatography, ion exchange chromatography, reversed phase chromatography, isoelectric focusing (IEF) and high performance liquid chromatography(HPLC). IGF I of specific activity 89 U/g, as measured by the isolated rat adipocyte assay, and IGF II, of specific activity 78 U/g, were obtained in yields of 16 micrograms and 34 micrograms respectively per 100g of Cohn fraction. Although this process yields IGF I which is contaminated with IGF II (due to the relatively large amount of the latter present in the original plasma), the IGF II preparations appear to be relatively free from IGF I. This separation was mainly achieved with IEF since the two factors elute close together on HPLC. Nevertheless, HPLC is important for their subsequent purification. The process is thus especially suitable for the preparation of IGF II and appears to give better yields than those obtained by earlier methods which used acid-ethanol extraction, gel permeation chromatography and polyacrylamide gel electrophoresis.