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Several fragments representing progressively shorter segments of the amino terminal region of bovine parathyroid hormone have been prepared by solid-phase peptide synthesis and bioassayed in the in vitro rat kidney adenyl cyclase assay and the in vivo chick hypercalcemia assay. These studies have denned the minimum chain length required for activity. The synthetic amino terminal 1-34 peptide was highly potent (80% on a molar basis of the natural hormone in vitro and 130% in vivo). It was found that deletion of the amino terminal residue (alanine) resulted in a marked decrease in activity and removal of the second residue (valine) at the amino terminus completely abolished activity in both assay systems. Greater shortening was tolerated at the carboxyl terminus. Peptide 1-27 was still active in the in vitro assay; deletion of residue 27 led to loss of biological activity in both assays. (Endocrinology93: 1349, 1973)
Tregear et al. (Sat,) studied this question.