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JBC, Vol. 251, Issue 1, 159-164, Jan, 1976
M. Rosenblatt, D. Goltzman, H. T. Keutmann, G. W. Tregear and J. T. Potts Jr
Several analogues of the biologically active fragment of bovine parathyroid
hormone (bPTH), based on the sequence of the NH2-terminal 34 amino acids,
were prepared by solid phase synthesis and bioassayed in the in vitro
adenylyl cyclase assay to provide further information concerning
structure-activity relations in parathyroid hormone. In two analogues both
methionines of the natural hormone were replaced with the sulfur-free and
closely isosteric amino acid norleucine (Nle). The synthetic analogue
[Nle-8, Nle-18]bPTH-(1-34) was highly active in the in vitro rat adenylyl
cyclase bioassay, thus demonstrating that neither of the methionines, found
in the native sequence, is indispensable for biological activity. Tyrosine
was substituted for phenylalanine at position 34 in the synthesis of two
other hormone analogues, [Try-34]bPTH-(1-34) and
[Nle-8,Nle-18,Tyr-34]bPTH-(1-34). Both derivatives were exposed to
conventional iodination procedures involving use of the oxidant chloramine
T. Although iodination of [Try-34]bPTH-(1-34) resulted in virtually
complete loss of biological activity, [Nle-8,Nle-18,Tyr-34]-bPTH-(1-34),
which lacks methionine, could be exposed to oxidants and labeled
efficiently with iodine with retention of nearly complete biological
activity. These findings confirm that the loss of biological activity after
oxidation of bPTH, as previously observed with the native hormone, is
indeed attributable to the oxidation lability of methionine rather than to
any other modifications. This sulfur-free, radioiodinated, biologically
active analogue of parathyroid hormone may prove useful in studies of
interaction of the hormone with the membrane receptors of target tissues
and in studies of the metabolism of parathyroid hormone.
Chemical and biological properties of synthetic, sulfur-free analogues of parathyroid hormone
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