Characterization of the sex steroid binding protein of human pregnancy serum. Improvements in the purification procedure

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Abstract
The sex steroid binding protein (SBP) of human pregnancy serum was purified to homogeneity by the sequential use of ammonium sulfate precipitation, affinity chromatography on 5.alpha.-dihydrotestosterone-17.beta.-succinyldiaminoethyl-(1,4-butanediol diglycidyl ether)-agarose and preparative polyacrylamide gel electrophoresis. The yield of pure SBP was improved from 5% as originally reported to 34%. Homogeneity of SBP was shown by equilibrium sedimentation ultracentrifugation in 6 M guanidine hydrochloride containing 0.1 M mercaptoethanol which yielded a minimum MW of 36,335 .+-. 525. The protein was also homogeneous when examined by gel electrophoresis in the presence of sodium dodecyl sulfate. A value of 52,000 for the MW was obtained by this method. SBP partially purified from Cohn fraction IV also had a MW of 52,000 by gel electrophoresis in the presence of sodium dodecyl sulfate; that fraction was contaminated with another protein of MW 90,000 which must be removed to obtain homogeneous SBP. The amino acid composition of SBP isolated from pregnancy serum was presented.