Isolation of human growth hormone isohormones D and E in milligram amounts (II), using isoelectric focusing on polyacrylamide gel.

Human growth hormone (hGH) isohormones D and E were prepared from a partial enzymatic hydrolyzate catalyzed by plasmin, using isoelectric focusing on polyacrylamide gel to fractionate the digest. Separation between the two isohormones species was optimized by employing a maximally flattened pH gradient between pH's 4.3 and 5.6. Gel slices containing isohormones D and E were extracted and concentrated by Steady-State Stacking on polyacrylamide gel. The extract was purified by gel filtration and lyophilized. Overall yields of lyophilized isohormones D and E were 10.9 mg and represented a recovery of 51% relative to the densitometrically estimated isohormone concentrations in the hGH digest. Purity of the products, based on Lowry analysis, U.V. absorbance and radioimmunoassay (RIA) was 60-70%. The isolated isohormone species were active in the rat tibia-line assay and in the specific RIA for hGH.