Molecular Pharmacology, Vol 1, 47-52, Copyright © 1965 by the American Society for Pharmacology and Experimental Therapeutics

Human Pituitary Growth Hormone XI. Rate of Hydrolysis by Trypsin, Chymotrypsin, and Pepsin; Effect of Trypsin on the Biological Activity

¹ Hormone Research Laboratory, University of California, Berkeley, California

Human pituitary growth hormone (HGH), both native and oxidized, has been subjected to hydrolysis with chymotrypsin, trypsin, and pepsin. With chymotrypsin and trypsin, the course of enzymic digestion was followed in the pH stat by recording the alkali uptake during digestion, and in addition, quantitative information about the dinitrophenylation of the digestion products was obtained. Hydrolysis of HGH with chymotrypsin was completed in 12 hr at 32° and with trypsin in 20 hr at 37°. With pepsin, a different procedure was followed; the rates of peptic digestion for varying lengths of time were studied, and the number of NH₂-terminal residues released was determined by quantitative dinitrophenylation in the pH-stat.

The NH₂-terminal amino acids released by digestion with the three enzymes were identified by quantitative paper chromatography of hydrolyzates of the dinitrophenylated digestion products. The effect of trypsin on the biological potency of HGH has also been investigated. It was found that partial hydrolysis of the hormone with trypsin does not diminish the growth-promoting and lactogenic activities.

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ACKNOWLEDGMENTS This work was supported in part by grants from the American Cancer Society and from the estate of L. D. Lasker, New York City, as well as by a travel grant to G. S. from the Swedish National Science Research Council.