No abstract

Recombinant DNA techniques were used to analyze the structure of the messenger RNA encoding a precursor of calcitonin, a small calcium-regulating hormone of 32 amino acids. Analyses of the nucleotide sequences of cloned complementary DNA's comprising the entire coding sequence of the messenger RNA revealed that calcitonin is flanked at both its amino and carboxyl termini by peptide extensions linked to the hormone by short sequences of basic amino acids. The location of glycine next to the carboxyl terminal prolinamide of calcitonin is consistent with indications that glycine is required for the enzymatic amidation of proline to the prolinamide. During cellular biosynthesis, calcitonin arises from a large precursor protein by cleavages at both amino and carboxyl terminal residues of the hormone. These findings raise questions concerning the regulation of these cleavages and the potential biological functions of the precursor extensions derived from these cleavages.

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The aminoterminal 1 -34 sequence of human parathyroid hormone (HPTH) has been synthesized by the solid-phase procedure. The synthetic peptide was found to be biologically active in both the /// vitro rat renal adenylate cyclase assay (1030 U/mg) and the in vivo chick hypercalcemic assay (7400 U/mg). The lower potency of the synthetic human 1-34 peptide in the adenylate cyclase assay compared to the corresponding synthetic bovine 1 -34 parathyroid hormone (5400 U/mg) most probably arises because of the presence of serine rather than alanine at position l in t he sequence. The synthetic analogue [Ala 1 ]HPTH-(l-34) was prepared and found to be significantly more active in the adenylate cyclase assay (4085 U/mg), confirming the importance of the Ala 1 position in the renal in vitro assay. The human and bovine 1-34 peptides were equipotent in the chick hypercalcemia assay. Immunological studies showed that on a molar basis the synthetic human 1-34 peptide and the native HPTH-(1 -84) were equipotent in displacing 125