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The preparation and properties of porcine neurophysin and the influence of calcium on the hormone‐neurophysin complex
Author(s) -
Ginsburg M.,
Jayasena K.,
Thomas P. J.
Publication year - 1966
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1966.sp007921
Subject(s) - neurophysins , oxytocin , vasopressin , chemistry , calcium , lysine , hormone , biochemistry , peptide , medicine , peptide hormone , endocrinology , amino acid , biology , organic chemistry
1. The preparation of a hormone‐binding protein fraction (neurophysin) from porcine neurohypophyses is described. 2. It was shown by gel‐filtration that the protein (which sedimented as a single component on analytical ultracentrifugation) forms complexes with oxytocin and lysine vasopressin. The maximum capacity of porcine neurophysin to bind oxytocin and lysine vasopressin was estimated from the results of dialysis experiments as 232 u. oxytocin and 48 u. lysine vasopressin/mg protein. 3. Binding of oxytocin and lysine vasopressin by neurophysin was completely inhibited in the presence of calcium in concentrations greater than 10 −6 M but is unaffected at less than 10 −7 M ‐Ca. The concentration of calcium required to inhibit binding did not appear to be dependent on hormone or protein concentrations. 4. No evidence was obtained that calcium was bound by neurophysin or by the peptide hormones either alone or in combination. 5. These results are discussed in the light of the hypothesis that release of the hormone from the neurohypophysis is mediated by calcium.