Production and Isolation of Recombinant Somatomedin C

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Abstract
High-level production of a growth promoting peptide hormone somatomedin C (insulin-like growth factor 1) has been achieved using recombinant DNA techniques in Escherichia coil. We found a new structural protein, designated as LH, to sta bilize somatomedin C in vivo, and constructed expression vectors for somatomedin C fusing to LH through a methionine and through a tryptophan, respectively. Each of the fused proteins was produced at approximately 4.5 × 105 molecules per single E. coil cell and comprised more than 20% of the total cellular proteins. Somato medin C was obtained in high yield by limited cyanogen bromide degradation of the methionine-type fused protein, in spite of somatomedin C itself having a Met at the 59th position, followed by renaturation of the resultant reduced peptide. The tryptophan-type fused protein was also converted to the peptide hormone by treating with 3-bromo-2-nitrophenylsulphenyl skatole or N-chlorosuccinimide. The recombinant somatomedin C obtained by these procedures was identical with the native one in amino acid sequence as well as in biological activity of stimulation of DNA synthesis in BALB/c 3T3 cells.