The sulfhydryl group is ubiquitous in proteins and mostly found in the oxidized form as disulfide linkages. The disulfide linkages contribute to the tertiary and quaternary structures of proteins. The spatial structure is the most important characteristic of the estrogen receptor (ER). The aim of the present analysis was to measure the -SH groups levels in estrogen receptors at increasing ligand concentrations.
The study was performed on cytosolic ER+ proteins isolated from tissue mouse mammary tumors of mice C3H/Sn, proteins isolated from nonlinear rat uterus and lyophilized receptors from DRG Instruments (Germany). 3H-estradiol 23 Сi/mM (England), diethylstilbestrol. Determination of -SH groups in proteins was performed by biochemical method using Elman's reagent. Proteins without denaturation and denatured with methyl alcohol were used.
A nonlinear hyperbolic relationship between increasing estrogen doses and the level of -SH groups is observed in lyophilized receptor proteins and those isolated from ER+ mouse mammary tumors of the C3H/Sn line and uterus of rats. In denatured receptor proteins, the level of –SH groups did not depend on the concentration of ligands, but was at a higher level than in native proteins. Obviously, different concentrations affect the conformational properties of a protein molecule, the change of which is nonlinear. The level of –SH groups in non-receptor proteins is much lower and is a maximum of 190 μM/l against 310 μM/l in receptor proteins. The technique without denaturants is more suitable for studying the functional properties of molecules. Cyclic changes in the concentration of –SH groups of receptor proteins at linearly increasing concentrations of diethylstilbestrol 0; 25; 50; 100; 200 nM were also detected in the cell-free system.
Receptor positive proteins have higher levels of sulfhydryl groups compared to non-receptor ones. The change in the level of –SH groups at increasing hormone concentrations is characteristic of both standard lyophilized receptors and receptors isolated from the uterus of rats, as well as from experimental ER+ mouse mammary tumors of C3H/Sn line.
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NAS of Ukraine.
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The author has declared no conflicts of interest.