JBC, Vol. 253, Issue 12, 4266-4269, Jun, 1978
Steroid modulation of human serum albumin binding properties. A spin label study
B. J. Soltys and J. C. Hsia
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-dinit
robenzene) 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.