Abstract
The binding isotherm and unique electron spin resonance spectral characteristics of a monoanionic spin label (1-gamma-aminobutyrate-5-N-(1-oxyl-2,2,6,6-tetramethyl-4-aminopiperidinyl)-2,4-dinitrobenzene) and a dianionic spin label (1-glutamate-5-N-(1-oxyl-2,2,6,6-tetramethyl-4-aminopiperidinyl)-2,4-dinitrobenzene) are used to prove the steroid modulation of serum albumin binding properties. Effects of a selected number of steroids (progesterone, testosterone, estradiol, aldosterone, estriol, corticosterone, deoxycorticosterone, hydrocortisone, and cortisone) on the binding isotherm of the monoanionic spin label binding to serum albumin have been determined. At the steroid/albumin ratio of 0.5 to 1, progesterone, testosterone, and estradiol enhance binding of the spin label at all concentrations studied. However, the remaining steroids exert an inhibitory effect at low spin label/albumin ratios and an enhancement effect at high spin label/albumin ratios. Progesterone and cortisone effects on the resonance spectra of the spin label bound to serum albumin confirm the enhancement and displacement properties of these ligands. Thus, like fatty acids, steroids may bind to either the primary or secondary bilirubin binding sites and also allosterically perturb the binding properties of serum albumin. The in vivo importance of the steroid-albumin interaction is discussed.
Highlights
From the Department of Pharmacology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada, M5S IA8
Progesterone and cortisone effects on the resonance spectra of the spin label bound to serum albumin confirm the enhancement and displacement properties of these ligands
We report here the steroid effects on the binding of two spin-labeled probes: l-yaminobutyrate-5-N-( l-oxyl-2,2,6,6-tetramethyl-4-aminopiperidinyl)-2,4-dinitrobenzene (GABA-DNB-SL)’
Summary
Of Human Serum Albumin Binding Properties (Received for publication, December 27, 1977). At the steroid/albumin ratio of 0.5 to 1, progesterone, testosterone, and estradiol enhance binding of the spin label at all concentrations studied. Progesterone and cortisone effects on the resonance spectra of the spin label bound to serum albumin confirm the enhancement and displacement properties of these ligands. We report here the steroid effects on the binding of two spin-labeled probes: l-yaminobutyrate-5-N-( l-oxyl-2,2,6,6-tetramethyl-4-aminopiperidinyl)-2,4-dinitrobenzene (GABA-DNB-SL)’. This is the fourth report in a series aimed at the resolution of serum albumin structure and function. ’ The abbreviations used are: GABA-DNB-SL,l y-aminobutyratemate-5-N-(l-oxyl-2,2,6,6-tetramethyl-4-aminopiperidinyl)2,4-dinitrobenzene ( Glu-DNB-SL) These spin-labeled probes have been shown to bind to the endogenous bilirubin binding sites of albumin [4, 5]. The observed net steroid effect depends on the degree of enhancement uersus inhibition behavior characteristics
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