Steroid-protein interactions. 42. Purification and characterization of the corticosteroid-binding globulin of pregnant guinea pig serum

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Abstract
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 MW 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.degree. C are 2.5 .times. 107 and 1.5 .times. 106 M-1 for cortisol and 1.4 .times. 106 and 0.2 .times. 106 M-1 for progesterone, respectively.