Purification and characterization of androgen binding protein from the rat epididymis

Androgen binding protein (ABP) was purified from rat epididymides by sequential ammonium sulfate precipitation, affinity chromatography, gel filtration, and DEAE ion exchange chromatography. The column matrix formed by coupling dihydrotestosterone-17 alpha-(hexanoic acidY to agarose via diisopropylamine was stable during the extensive washing required following application of crude tissue extracts to the affinity matrix. In addition, when used under the optimal conditions, the column produced a 1600-fold purified in a single step. Apparent homogeneity of the final product was shown by polyacrylamide gel electrophoresis, sedimentation equilibrium, and constant specific activity across the peak of the final chromatograph. The molecular weight determined by sedimentation equilibrium at pH 7.4 was 85 000. By contrast, the molecular weight determined by sedimentation equilibrium in guanidine.HCl and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis was approximately one-half that of the native protein, suggesting that suggesting that ABP is comprised of subunits.