Some Properties of a Testosterone-binding Component of Human Pregnancy Serum

Determination of Sex Hormone-binding Globulin in Human Semen by Selective Ammonium Sulphate Precipitation*

A simple method was developed to measure the SHBG capacities of human serum, semen and sperm cells. After suitable dilution, disintegration and addition of labelled dihydrotestosterone-1,2-3 H or testosterone-1,2-3 H, the SHBG was precipitated by the addition of saturated ammonium sulphate in a final concentration of 42.3%. The precipitate was centrifuged and the activity of the non-bound, labelled steroid was counted in an aliquot of the supernatant. Subtraction of this result from the total activity yielded the SHBG-bound steroid in microgram/100 ml or nmol/l. Examination of 52 males gave normal values of means = 13.91 nmol/l (S.E.M. = 0,746) dihydrotestosterone binding globulin (DHTBG) and means = 11.67 nmol/l (S.E.M. = 0.555) testosterone binding globulin (TBG) in serum, while the concentrations in the seminal plasma were means = 10.89 nmol/l (S.E.M. = 0,723) DHTBG and means = 8.93 nmol/l (S.E.M. = 0.625) TBG. means = 5.57 ng/mg protein (S.E.M. = 0.516) DHTBG and means = 4.91 ng/mg protein (S.E.M. = 0.440) TBG were found in the disintegrated sperm cells.

The plasma sex steroid binding protein (SBP or SHBG). A critical review of recent developments on the structure, molecular biology and function

Significant developments have taken place within the past five years on the characterization, molecular biology and function of the plasma sex steroid-binding protein, SBP (or sex hormone binding globulin, SHBG). During the span of that time, amino acid sequences of two SBPs have been established, amino acid residues in the steroid-binding site have been identified, the structure of the human SBP gene has been deduced and evidence for the possible existence of a SBP membrane receptor has been presented. This review covers the salient aspects of these and other developments including a critical analysis of the various proposed models and interpretations with regards to the structure, evolution, molecular biology and function of SBP.

Progesterone-binding protein in the corpus luteum, blood and lymph of sheep

A protein which binds progesterone but not cortisol was found in luteal cytosol, utero-ovarian venous plasma, ovarian lymph and jugular venous plasma of sheep. The protein was isolated from other steroid-binding activities present in luteal cytosol and plasma by de-adsorption from hydroxyapatite with 40 mM phosphate. In all cases, it bound progesterone at 4 degrees C with an equilibrium affinity constant of the order of 10(6) l/mol, but did not bind cortisol. After chromatography on hydroxyapatite and Sephadex G-200, the protein obtained from utero-ovarian venous plasma had lost much of its steroid-binding activity, but migrated as a monomer of molecular weight 64 000 in polyacrylamide gel. Bovine luteal cytosol is reported to contain two proteins which bind progesterone similarly. In ruminants, these proteins may participate in the biosynthesis and secretion of progesterone from luteal cells and its transport in blood.

Sex hormone binding globulin and transcortin in human and baboon males

TeBG and transcortin were identified in serum from adult male baboons. TeBG values were higher than the TeBG concentration in adult men. The relative competitive abilities of three natural steroids, a synthetic androgen and two synthetic estrogens, for binding sites on TeBG occupied by radioactive DHT were compared. At a 10-fold molar excess, using both baboon and human TeBG, DHT and T were the most effective competitors; E2 was intermediate and DES a very poor one. Using gel filtration, the transcortin concentrations (mg/L) in two baboons were 16.8 and 27.4; the normal range for men is 23--45. The serum transcortin value of a third baboon, determined by equilibrium dialysis, was 0.41 micron/L (21.5 mg/L). Competition studies, using both techniques, showed that progesterone has a slightly higher affinity for baboon transcortin than cortisol and that a synthetic progestin does not bind to transcortin. Plasma binding capacity for synthetic steroids should be tested before they are used for studies on specific tissue receptors contaminated with serum.

Maternal and fetal serum levels of total cortisol and cortisone, unbound cortisol, and corticosteroid-binding globulin in vaginal delivery and cesarean section

The levels of corticosteroid-binding globulin (CBG, transcortin), total cortisol, and unbound cortisol were measured in maternal and fetal serum at the time of cesarean section or vaginal delivery. While the total cortisol levels in maternal serum do not differ significantly in vaginal delivery as compared to cesarean section, cord serum cortisol levels are significantly higher after vaginal delivery. There are no differences associated with the route of delivery between the mean levels of CBG in cord and maternal blood. However, after the vaginal delivery the unbound cortisol level in maternal serum is more than twice as high as that at cesarean section and in cord serum it is seven times as high. These changes reflect changes in total cortisol and may represent a prelabor surge of fetal cortisol production, or a stress response associated with labor, or a combination of both.

Binding of norgestrel to human plasma proteins

Binding of [14, 15-3H](+/-)-norgestrel to human plasma proteins has been investigated. Norgestrel showed greater affinity to plasma than to human serum albumin indicating specific norgestrel binding protein(s) in the plasma. alpha1-acid glycoprotein showed high affinity for norgestrel when compared with human serum albumin. The binding protein was eluted at pH 5.8 by step by step elution on a DEAE-cellulose column. Norgestrel binding to plasma proteins was not affected at 60 degrees C. The optimal binding occurred between pH 7 and 8. Ligand specificity of the binding protein revealed that progesterone was able to compete for the norgestrel binding sites, whereas corticosterone, testosterone, oestradiol, and norethindrone acetate did not show much competition. The molecular weight of the binding protein was found to be approximately 43 000. Sucrose density gradient analysis indicated that norgestrel bound to a macromolecular component of sedimentation coefficient 2.9 S. The association constant (Kass) and dissociation constant (Kdiss) of norgestrel-binding plasma protein was found to be 1.4-10(6) M-1 and 0.7-10(-6) M respectively. The number of binding sites was 0.5-10(-9) mol/mg protein. Norgestrel-binding protein in the plasma appeared to be a protein different from human serum albumin, corticosteroid-binding globulin and sex-steroid-binding protein. This binding protein showed some similarities to alpha1-acid glycoprotein.

Steroid-binding proteins in rabbit plasma: Separation of testosterone-binding globulin (TeBG) from corticosteroid-binding globulin (CBG), preliminary characterization of TeBG, and changes in TeBG concentration during sexual maturation

Two distinct steroid-binding proteins are present in rabbit plasma. One of the proteins (TeBG) binds [3-H]5 alpha-dihydrotestosterone (5 alpha DHT) and [3-H]testosterone. The affinity of this binding protein for 5 alpha DHT was 3-4 times greater than for testosterone. Binding of [3-H]5 alphaDHT could be inhibited by unlabeled 5 alpha DHT, testosterone, 5 alpha-androstan-3 alpha,17 beta-diol (3 alpha-diol), and 17 alpha-methyl- B-testosterone (skf) 7690). The relative affinity of the competitors was: 5 alpha DHT greater than 3 alpha-diol greater than testosterone greater than SKF 7690. The antiandrogens, cyproterone (1,2 alpha-methylene-6-chloro-pregn-4,6-diene-17 alpla-ol-3,20 dione), cyproterone-17-acetate, and 6 alpha-bromo-17 beta-hydroxy-17 alpha-methyl-4-oxa-5 alpha-androstan-3-ine (BOMT) were ineffective in competing for [3-H5d alpha DHT binding sites, as were 4-androstene-3, 17-dione, 17 beta-estradiol (E2), progesterone, and cortisol. The formation of the [3-H]5 alpha DHT-TeBG complex was extremely rapid; the binding reaction was essentially completed in 15 s. The complex dissociated rapidly in the presence of charcoal. The dissociation rate constant (Kdiss) was 0.157 min- minus 1 and the dissociation half-time t-1/2) was 4.5 min. In the presence of charcoal and unlabeled 5 alpha DHT the Kdiss was 0.268 min- minus 1 and the t=1/2 was 2.6 min. The sedimentation coefficient of TeBG was congruent to 4.6 S and its molecular weight, estimated by gel filtration on a calibrated Sephadex G-200 column, was congruent to 75,000. The concentration of TeBG in male rabbit plasma decreased with sexual maturation and was approximately three times higher in adult females than in adult males. The other protein (CBG) bound both [3-H]cortisol and [3-H]progesterone. Binding of these compounds could be inhibited by unlabeled cortisol and progesterone, but not by unlabeled 5 alpha DHT, testosterone, or E2. CBG had a sedimentation of congruent to 3.9 S and an apparent molecular weight of congruent to 105,000. TeBG could be separated from CBG by a 60% ammonium sulfate precipitation and by gel filtration chromatography. Both proteins are thermolabile; TeBG is inactivated at temperatures above 30 degrees C and CBG is inactivated at temperatures above 50 degrees C.

Purification of the sex steroid binding protein from human serum

The sex steroid binding protein from human pregnancy serum was purified to homogeneity by affinity chromatography and preparative polyacrylamide gel electrophoresis. The selective adsorbants were prepared by coupling [3H]-5alpha-dihydrotestosterone 17beta-hemisuccinate to 3,3'-diaminodipropylamine-agarose, poly(Lys-DLAla)-agarose, and albumin-agarose. The most effective adsorbant purifying for the binding protein was 5alpha-dihydrotestosterone 17beta-hemisuccinyl-3,3'-diaminodipropylamine-agarose. A preparative procedure with 5alpha-dihydrotestosterone 17beta-hemisuccinyl-3,3'-diaminodipropylamine-agarose yielded active material which was further purified by preparative polyacrylamide electrophoresis at pH 9.5. Homogeneity was shown by analytical disc gel electrophoresis at three different pH units. A single radioactive band corresponding to the stained band was shown by incubating with [1,2-3H]-5alpha-dihydrotestosterone prior to electrophoresis. The radioactive peak corresponding to the pure sex steroid binding protein could not be detected when a 100-fold excess of 17beta-estradiol was present in the incubation prior to electrophoresis demonstrating the specific sex steroid binding properties of this protein. The migration of this peak was identical with that obtained when diluted serum was electrophoresed under the same conditions in the presence of [1,2-3H]-5alpha-dihydrotestosterone indicating that no significant changes in the molecular characteristics of the binding protein occurred during the purification procedure. The presence of carbohydrate in the pure protein was shown by the periodic acid-Schiff reagent procedure. Selective adsorbants containing 17beta-estradiol linked at the 3 position were ineffective in retaining sex steroid binding protein activity.