PMID: 9191984Feb 1, 1997Paper

Isotope effect in the binding of tritium and 14C-labelled cortisol to corticosteroid-binding-globulin in serum

The Journal of Steroid Biochemistry and Molecular Biology
E G LentjesA J Moolenaar

Abstract

We have determined the free cortisol concentration in serum using either the Amicon MPS-1 ultrafiltration-centrifugation method (I) or equilibrium dialysis (II). If procedure I was used we found that [1,2,6,7-3H]-, and [4-14C]cortisol had a lower affinity than unlabelled cortisol for corticosteroid binding globulin (CBG). The binding affinity (Ka) to three separate CBG-containing samples was 8-18 times lower for [1,2,6,7-3H]cortisol and 30-90 times lower for [4-14C]cortisol, when compared with that of unlabelled cortisol. This difference in affinity to CBG was not observed if method II was used for the free cortisol determinations. The observed isotope effect in method I is not caused by unspecific binding to material such as the Amicon MPS-1 chamber or to impurities in the tracer. We suggest that the centrifugation step during ultrafiltration changed the conformation of CBG, thereby reducing its affinity for labelled cortisol. It is concluded that incorrect results will be obtained if radiolabelled is cortisol used for determining the free cortisol content of plasma with the Amicon MPS-1 device.

References

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Citations

Jul 16, 2013·Chemical Reviews·Katarzyna Swiderek, Piotr Paneth
Sep 5, 2015·Endocrine Practice : Official Journal of the American College of Endocrinology and the American Association of Clinical Endocrinologists·Irina BancosRavinder Singh
Apr 13, 2007·Clinical Biochemistry·Michael Vogeser, Josef Briegel
Feb 22, 2011·Clinica Chimica Acta; International Journal of Clinical Chemistry·Carel J PretoriusJacobus P J Ungerer
Oct 19, 1999·Statistics in Medicine·J M OlsonR C Elston

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