The chemistry of human transcortin. The effects of pH, urea, salt, and temperature on the binding of cortisol and progesterone

Daniel W. Chan, W. R. Slaunwhite

Research output: Contribution to journalArticlepeer-review

Abstract

The interaction of cortisol and progesterone with pure transcortin was investigated. The temperature dependence of cortisol and progesterone binding is a result of the predominantly negative enthalpy of binding which suggests a very good fit between ligand and protein such that the bonds formed are of the van der Waals type. The optimal pH of cortisol (8.0) and progesterone (8.5) binding suggests involvement of cysteine, histidine, and/or tyrosine residues in the binding process. Transcortin is irreversibly denatured at pH 4.0. The effect of sodium chloride on the binding of both steroids is small. At lower sodium chloride concentrations (less than 0.15 m), binding decreases somewhat with decreasing salt concentration. Urea produces a progressive decrease in the association constants of both steroids which is completely reversible up to 2.0 m and 30% reversible at 3.0 m. Scatchard analysis of cortisol binding in the presence of a constant amount of progesterone and vice versa confirms earlier data obtained on plasma that cortisol and progesterone do not bind at two independent sites. It is not possible, however, to decide whether they bind at the same site or at two interdependent (interacting) sites.

Original languageEnglish (US)
Pages (from-to)437-442
Number of pages6
JournalArchives of Biochemistry and Biophysics
Volume182
Issue number2
DOIs
StatePublished - Aug 1977
Externally publishedYes

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology

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