Evidence for structural dissociation of two biologic actions of growth hormone

Effect of unilateral ureteral obstruction on renal polyamine levels in rats

Unilateral ureteral obstruction in rats, resulted in considerable alterations of polyamine levels in the obstructed kidney during a 72-h observation period, as compared with respective values for the contralateral control kidney.

Comparative conformational analysis of human choriomammotropin and somatotropin from several species

The conformations of porcine somatotropin and human choriomammotropin have been studied using circular dichroism (CD) and the results compared with spectra of human, murine, ovine, and bovine somatotropin. The far ultraviolet CD spectra of the six proteins were similar, and each spectrum was analyzed using constrained linear least squares. The following average percentages of alpha-helicity, beta-structure, and aperiodic (nonhelical) conformation were obtained: 57, 6, and 37, respectively, based on a standard protein reference set, and 42, 22, and 36, respectively, based on poly-L-lysine as reference. Thus, the estimated secondary structure is strongly dependent upon the reference data used. Interestingly for these similar proteins, it appears that over 60% of the residues are part of ordered secondary structure and less that 40% are in an aperiodic conformation. The near ultraviolet CD spectra of these hormones were similar in many respects, although certain significant differences were observed, particularly in the sign of various extrema. These spectral differences probably reflect non-identical microenvironments of the aromatics and disulfides, arising from differences both in amino acid sequence and local conformation.

Somatostatin conformation: evidence for a stable intramolecular structure from circular dichroism, diffusion, and sedimentation equilibrium

Somatostatin is a hypothalamic tetradeca peptide that inhibits the release of growth hormone insulin, and glucagon. The circular dichroism spectrum is characterized by negative extrema at 238 nm and 270 nm, and a positive extremum at 225 nm. The far ultraviolet circular dichroism spectrum is consistent with the presence of ordered secondary structure such as beta-structure, but not alpha-helix. Sedimentation equilibrium results demonstrate that somatostatin exists in its monomeric form (i.e., a molecular weight of 1610 +/- 36 was obtained) and, thus, the structure must arise from intramolecular interactions. The diffusion constant of somatostatin was estimated to be 1.66 X 10(-6) cm2/sec. These data are consistent with an ellipsoidal rather than a spherical shape. The magnitude of the ellipticity at both 225 nm and 238 nm is quite dependent on guanidinium hydrochloride concentration; the midpoint occurs at about 3 M and the transition is cooperative-like. These data strongly suggest that somatostatin has a stable conformation in aqueous solution. A model, consistent with the results of the physicochemical studies and with semi-empirical rules for secondary structure formation, is proposed for somatostatin. The proposed structure consists of a hairpin loop with several residues in an antiparallel beta-pleated sheet, is somewhat elongated, and contains a hydrophobic domain at one end and a hydrophilic domain at the other end.