Certain structural features of bovine proparathyroid hormone, the known biosynthetic precursor to parathyroid hormone, could be determined by chemical and enzymatic cleavage of the radioactive prohormone. Electrophoretic and chromatographic mobilities of amino–terminal fragments of labeled proparathyroid hormone derived by limited cleavage with cyanogen bromide or dilute acid were found to differ from those of parathyroid hormone. However, the mobilities of carboxyl–terminal tryptic fragments of proparathyroid hormone and parathyroid hormone were identical. The results indicate that the additional amino acids of proparathyroid hormone are at the amino-terminal and not the carboxyl–terminal end of the hormone. Amino–terminal tryptic fragments of proparathyroid hormone were found to be identical indicating that an arginine or lysine residue must be present in the prohormone sequences close to the amino–terminal alanine residue of parathyroid hormone.
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