Preliminary Investigations on the Action of Pepsin on Human Pituitary Growth Hormone

A slight modification of the original procedure for the isolation of human pituitary growth hormone has been described. The purity of the preparation was further examined by chromatography on carboxymethylcellulose, zone electrophoresis on starch, and electrodialysis. The hormone was found to be stable in a pH 7.0 solution at 100°C and in 10 M urea at 25°C. Digestion with pepsin to an extent of 40 per cent did not diminish the biological activities of the hormone. Bioassays of an active core derived from such digests exhibited essentially the same specific growth-stimulating activity in the hypophysectomized rat and crop sac stimulation in the pigeon. It was concluded that the integrity of the protein is not required for the activity of human growth hormone.