The serum sex steroid-binding protein. Purification, characterization and immunological properties of the human and rabbit proteins

Abstract

This review describes the purification, characterization, and immunological properties of the sex steroidbinding protein (SBP) of human and rabbit sera. Both proteins were purified to homogeneity by the sequential use of ammonium sulfate precipitation, affinity chromatography on 5α-dihydrotestosterone-17β-succinyldiaminoethyl-(1,4-butanediol diglycidyl ether)-agarose, and polyacrylamide gel electrophoresis. An agarose gel filtration step was included in the case of rabbit SBP to remove contaminating lipoproteins. Recent observations indicate that attachment of the spacer “arm” at the 17α-position improves the affinity chromatography step. Human and rabbit SBP are glycoproteins having minimal molecular weights of 36,335 and 36,475, respectively. The amino acid compositions are similar, but the carbohydrate content of rabbit SBP is approximately twice that of human SBP (30-vs-18%). Monospecific antibodies prepared against homogeneous human SBP do not cross-react with rabbit, cat, dog, sheep, goat, cow, and calf sera. Cross-reactivity is demonstrated with Macaca nemestrina and Papio cynocephalus (baboon) sera suggesting a structural similarity between human, monkey, and baboon SBPs. The results indicate that these subhuman primates will serve as useful animal models for the study of the physiological role of SBP. Monospecific antibodies prepared against homogeneous rabbit SBP do not cross-react with human, monkey, baboon, cat, dog, sheep, goat, cow, and calf sera.