Synthetic parathyroid hormone-like protein-(1-74): biochemical and physiological characterization.

PTH-like protein-(1-74) [PTHLP-(1-74)] was synthesized and purified. On the basis of chromatographic criteria and amino acid composition of the full-length peptide, direct amino acid sequencing of the N-terminus, and amino acid composition and internal sequence of proteolytic fragments of PTHLP-(1-74), the synthetic peptide appears to be of high quality and purity. Physiological comparison of PTHLP-(1-74) to [Tyr36]-PTHLP-(1-36) amide and bovine (b) PTH-(1-34) indicates that all three peptides are of equivalent potency in the fetal rat long bone and rat osteosarcoma 17/2.8 adenylate cyclase assays. However, as in earlier studies with native and N-terminal PTHLPs, PTHLP-(1-74) is considerably less potent (2%) in stimulating the canine renal cortical adenylate cyclase assay than is bPTH-(1-34). Further, PTHLP-(1-74) displayed only 12% of the activity of bPTH-(1-34) in inducing hypercalcemia when infused into rats in vivo. These studies support the possibility that subclasses of PTH receptors or varying PTH- and PTHLP-signalling transduction mechanisms may exist. In addition, they emphasize the need to precisely define the naturally occurring secretory and circulating species of this novel class of peptide hormones.