Preparation and characterization of radioactive monoiodotyrosine and diiodotyrosine derivatives of parathyroid hormone

The beta-subunit of the bovine mitochondrial F1 ATPase specifically binds the amino terminal domain of parathyroid hormone

A protein which specifically binds the amino terminal domain of parathyroid hormone (PTH) on nitrocellulose blots of polyacrylamide gels was fragmented with cyanogen bromide (CNBr), and two fragments were sequenced through 20 residues. The sequence obtained was 100% homologous with the beta-subunit of bovine F1 mitochondrial ATPase. Purified F1 ATPase from bovine heart and Escherichia coli were obtained and the binding of PTH examined on the blots. The beta-subunit of the bovine enzyme bound PTH specifically through its amino terminal domain. However, both the alpha- and beta-subunit of the E. coli enzyme were found to bind the hormone. This binding was also specific for the amino terminal domain of the hormone. The subcellular distribution of the PTH-binding protein from bovine kidney was also examined further. While the mitochondria and plasma membrane appear to possess similar PTH-binding capability, submitochondrial particles enriched in F1 ATPase were also enriched in PTH-binding activity.

Separation of protein hormones

The purpose of this review is to highlight modern techniques in HPLC and electrophoresis used for protein hormone separations. The advent of biotechnological methods for production of synthetic polypeptides and recombinant proteins will have a significant future impact on the types of therapeutics and metabolites that need to be monitored in the clinical laboratory. The protein hormone examples given in this work were selected because of the comprehensive body of separation science literature and not necessarily for their future importance in medicine. The intention was to present an array of general methods and techniques which may be useful to the clinical investigator for analysis of any protein hormone.

Deletion of lysine 13 alters the structure and function of parathyroid hormone

A peptide of unknown structure was found as a side product in a commercial preparation of the 1-34 fragment of bovine parathyroid hormone (PTH). CNBr cleavage and amino acid analysis showed that this peptide is the des-lys-13 form of 1-34 bovine PTH. The peptide thus represents a deletion mutant of PTH and structure-function studies are of interest. This peptide was a full agonist in the adenylyl cyclase bioassay for PTH, but its potency was about 5% of that found for the complete 1-34 peptide. Proton NMR studies showed that the pK values for the histidine residues in the des-lys-13 form were essentially identical to those of the intact peptide. However, pH-dependent changes in the chemical shifts for the tryptophan protons (residue 23) and several unidentified methyl group resonances were observed in the des-lys peptide. The latter are major shifts and probably represent ring-current effects; these were not seen in the intact 1-34 peptide. The results show that Lys-13 is important in the folding of the active domain of PTH, and are interpreted in the context of a previously published model for the folding of this hormone.

Proton NMR studies of the biologically active 1-34 fragment of bovine parathyroid hormone: examination of a structural model

Proton NMR spectra of the biologically active 1-34 fragment of bovine parathyroid hormone (bPTH) were studied as a function of pH over the range of pH 4 to 10, in buffer and in 6 M guanidine DC1. One of the histidine C-2 peaks titrated normally, with a pKa value of 6.8, but the other two histidines in this peptide had pKa values of 6.3. Denatured PTH showed only one histidine C-2 peak with a pKa of 6.7. An aliphatic peak identified as due to either a methionine or a glutamine residue also shifted with pH, and the pKa for this shift was 6.3. Finally, small but significant upfield shifts in the methyl and methylene resonances were observed as a function of pH, and when compared to the denatured peptide. These results indicate that the N-terminal domain of native PTH has considerable structure in solution, and are consistent with a theoretical model for the folding of this peptide.

The role of the methionine residues in the structure and function of parathyroid hormone

Forms of the biologically active N-terminal fragment of bovine parathyroid hormone oxidized at methionine 8, methionine 18, and both positions were prepared, separated from one another, and characterized as described earlier for the native hormone (A. L. Frelinger and J. E. Zull, (1984) J. Biol. Chem. 259, 5507). The biological properties of the oxidized forms were compared to those of the native hormone, using the renal membrane adenylyl cyclase assay. Oxidation at position 18 produced full agonists of the hormone with slightly reduced potency. Oxidation at position 8 produced partial agonists of greatly reduced potency. Oxidation at both positions produced partial agonists of even lower potency. Thus, methionine 8 is implicated both in binding and in activation of adenylyl cyclase, but methionine 18 is implicated only in binding. Further study showed that oxidation of both residues is dependent on the pH, ionic strength, and polarity of the solvent. However, methionine 8 is less easily oxidized than methionine 18. This difference is eliminated in 3 M guanidine-HCl with 1-34 and in 6 M guanidine-HCl with 1-84. On the other hand the difference in reactivity is greatly increased in high ionic strength, with methionine 8 becoming much less reactive. These results suggest that the methionine residues are important in the biologically active conformation of parathyroid hormone and that methionine 8 is less accessible than methionine 18 under certain conditions. These conclusions are discussed in the context of a specific model for the folding of parathyroid hormone.