Steroid-Protein Interactions

Abstract

The species specificity which had been observed in rat and human "transcortin' for the species specific corticosteroid has not been found to be a general phenomenon. The corticosteroid-binding proteins in the sera of various mammalian species belong to the alpha globulin as was demonstrated by the method of equilibrium paper electrophoresis. Electrophoretic studies showed that the "transcortin" containing fraction of rat serum migrates faster than albumin at pH values below 7, whereas at higher pH it behaves as an alpha globulin.The al 1 -acid glycoprotein (orosomucoid) has been prepared by a combination of precipitation and chromatographic procedures. The interaction of progesterone with this glycoprotein has been found to be highly dependent on temperature; the association constant decreases with increasing temperature. A strong dependency on pH has also been observed; the association constant is highest at pH 8 and decreases to about 1/20 of this value at pH 2.3. The number of binding sites for progesterone has been determined to be n = 1 at pH 7.4, 4*C; the free energy of binding has the relatively high value of -7.5 kilocalories per mole. Partial removal of sialic acid from the orosomucoid preparations reduced the binding affinity for progesterone. In biological assay studies on the ligated uterus horn of the mouse it was observed that progesterone is inactivated by binding to the a,-acid glycoprotein.

Isolation, Characterization and Radioimmunoassay of Corticosteroid-Binding Globulin (Cbg) in Human Serum – Clinical Significance and Comparison to Thyroxine-Binding Globulin (Tbg)

“…The CBG levels in serum of healthy adults corresponded well with the values estimated by the earlier published methods (Westphal 1971;Rosner et al J973;Racadol ct al. 1974: Van Baelen Sc De Moor 1974Rosner 1976).…”

“…Gaillard et al 1975). By ultracentrifugation, we determined the value of 50 700, the sedimentation coefficient of 3.6 S and the partial specific volume of 0.690 ml/g, which corresponds to the values published by Westphal (1971 Gaillard et al 1975;Rosner 1976). …”

Spider Hemocyanin Binds Ecdysone and 20-OH-Ecdysone

“…Thus, the value for the dissociation constant obtained by fluorescence quenching should be larger than 0.5 mM. Second, similar low binding constants are reported for the binding of steroids to albumin, and two possible error sources are discussed (13), which may also be true for hemocyanin and may explain the difference in dissociation constants by 1 order of magnitude obtained with the two different methods. The presence of ethanol in the fluorescence quenching experiment may alter the steroid-hemocyanin interaction.…”

25-Hydroxycholecalciferol receptors in human breast cancer

“…Many substances bind specifically to cytosol receptors without apparent physiological affects (Funder, 1978). On the other hand, high circulating-oestrogen levels are associated with high circulating levels of 25-OHCC-binding protein ) and other carrier proteins (Westphal, 1971). It is therefore possible that intracellular receptors for oestrogen and 25-OHCC share similar controlling mechanisms.…”