Purification and partial characterization of a corticosteroid-binding globulin from hamster serum

Our objective was to characterize and purify the corticosteroid-binding proteins in hamster pregnancy serum. When [3H]cortisol-labeled pregnancy and proestrous serum were subjected to native polyacrylamide gel electrophoresis, a single peak of specific steroid-binding activity was detected in each, with identical electrophoretic mobility. The steroid-binding affinity (Ka = 1.07.10(8) M-1 for cortisol) is typical of corticosteroid-binding globulin from other species, but the steroid-binding specificity (cortisol greater than testosterone greater than progesterone) is not. An ultraviolet photoaffinity-labeling protocol was developed using 17 beta-hydroxy-4,6-[1,2-3H]androstadiene-3-one ([3H]androstadienolone), permitting analysis of ultraviolet photoaffinity-labeled proestrous and pregnancy serum by two-dimensional polyacrylamide gel electrophoresis and fluorography. Both sera contained the same labeled protein species. Corticosteroid-binding globulin was purified from pregnancy serum by DEAE-cellulose chromatography followed by steroid affinity chromatography on androstadienolone-17 beta-hemisuccinate-ethylenediamine-AffiGel 10. The purified protein (Mr = 62,250; pI = 3.95; n = 1; Stokes radius = 3.5; S = 4-5) was determined to be a glycoprotein. When analyzed by gel filtration and two-dimensional polyacrylamide gel electrophoresis, purified corticosteroid-binding globulin behaved the same as in unfractionated serum, and when ultraviolet photoaffinity-labeled with [3H]androstadienolone, purified corticosteroid-binding globulin produced the same fluorogram spot pattern seen in unfractionated serum. A specific corticosteroid-binding globulin antiserum was raised in rabbits, and this antiserum reacted with a single spot in Western blots of unfractionated serum. Thus, hamster pregnancy serum was determined to have one corticosteroid-binding protein. This protein is identical to the corticosteroid-binding globulin found in proestrous serum, with a higher titer in pregnancy serum. No other steroid-binding component is observed in hamster serum.     

Purification and characterization of testosterone-binding globulin of canine serum.

Testosterone-binding globulin (TeBG) of canine serum was purified to apparent homogeneity by affinity chromatography on testosterone-17 alpha-ethynylcarboxyaminoethyl-Sepharose 4B followed by hydroxyapatite column chromatography. Canine TeBG was a glycoprotein containing 5.5% carbohydrates. Equilibrium sedimentation analysis in the presence and absence of 6 M guanidine hydrochloride gave molecular weights of 40,000 and 76,000, respectively, suggesting that native TeBG consists of two subunits. Equilibrium dissociation constants at 0 degrees C for testosterone and dihydrotestosterone were estimated to be 5.58 x 10(-8) M and 1.43 x 10(-8) M, respectively, and the number of binding site per native molecule was approximately unity for both androgens. Canine TeBG had virtually no affinity for estradiol, progesterone, or cortisol. Canine TeBG did not cross-react with a rabbit antiserum raised against bovine TeBG.     

Purification and characterization of the corticosteroid-binding globulin of pregnant guinea pig serum.

The corticosteroid-binding globulin from guinea pig pregnancy serum was purified by the sequential use of affinity chromatography, hydroxylapatite chromatography, and gel filtration chromatography at a cumulative yield of 80%. The protein was found to be homogeneous by analytical gel electrophoresis, equilibrium sedimentation ultracentrifugation, immunoelectrophoresis, and stoichiometry (1:1) of steroid binding. Guinea pig corticosteroid-binding globulin has a molecular weight of 43 300 and contains 29% carbohydrate. The intrinsic fluorescence of the corticosteroid-binding globulin is quenched by about 73% when 1 mol of cortisol is bound. The association constants (pH 7.4) at 4 and 37 degrees C are 2.5 X 10(7) and 1.5 X 10(6) M-1 for cortisol and 1.4 X 10(6) and 0.2 X 10(6) M-1 for progesterone, respectively.     

The association of hereditary gamma globulin (a) activity with a fragment of human gamma globulin produced by papain digestion

The technique of enzymatic hydrolysis has been utilized to demonstrate that for the five sera investigated the determinant of Gm (a) specificity is confined to a 3.5S fragment of the human 7S gamma globulin molecule.