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

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.