HUMAN PITUITARY GROWTH HORMONE . PHYSICOCHEMICAL INVESTIGATIONS OF NATIVE AND REDUCED-ALKYLATED PROTEIN

Results of investigations into the biological and physicochemical properties of native, reduced-tetra-S-carbamidomethylated, and reduced-tetra-S-carboxymethylated human pituitary growth hormone are presented. While both derivatives appear to retain lactogenic activity, only the carbamidomethylated product retains growth-promoting potency. Measurements of chemical composition, molecular weight, viscosity, spectrophotometric titration of tyrosyl groups, and circular dichroism have failed to uncover any significant differences between the two derivatives. In addition, differences between either derivative and the native hormone appear to be very small. Accordingly, we conclude that the disulfide bonds in this molecule are not necessary for the manifestation of biological activity nor are they required for the formation of the secondary and tertiary structure. However, investigation of the relative rates of proteolysis by trypsin would indicate that the presence of these bonds does serve to stabilize the molecular architecture against perturbing forces. The carbamidomethylated derivative is digested about 1.5 times as fast as the native, while the carboxymethylated product, under identical conditions, is digested at 2.5-3 times the rate of the native hormone. © 1969, American Chemical Society. All rights reserved.