Purification and characterization of the sex steroid-binding protein of rabbit serum. Comparison with the human protein.

The sex steroid-binding protein (rSBP) of immature rabbit serum was purified to homogeneity by the sequential use of DEAE-cellulose chromatography, affinity chromatography on 5alpha-dihydrotestosterone-17 beta-succinyl-diaminoethyl-(1,4-butanediol diglycidyl ether)-agarose, agarose (Bio-Gel-A-0.5m) gel filtration, and preparative polyacrylamide gel electrophoresis. The cumulative yield is 13%. Homogeneity of rSBP was shown by the equilibrium sedimentation ultracentrifugation in 6 M guanidine HCl containing 0.1 M mercaptoethanol which yields an average molecular weight of 36,475 +/- 865. Analytical gel electrophoresis in the presence of sodium dodecyl sulfate and gel filtration on agarose yield a molecular weight of 57,000 and 120,000, respectively. The variation is due to a 30% carbohydrate content. The amino acid composition is reported. Comparison of the rabbit and human SBP indicate that they are different in both their molecular and functional properties.