title: Conformational changes in the progesterone binding globulin-progesterone complex.
abstract: An improved purification procedure for the progesterone-binding globulin (PBG) of the pregnant guinea pig has been developed utilizing sulfopropyl Sephadex, a strong cation exchanger, in the first step. The method exploits the low pI (2.8) and favorable acid stability of the glycoprotein. Subsequent chromatographies on DEAE-cellulose and Sephadex G-200 afford a highly purified PBG that exhibits the previously observed polydispersity (R.M. Burton et al. (1974), Biochemistry 13, 3554-3561). Circular dichroism, optical rotatory dispersion, and difference uv spectra all indicate the purified protein to undergo a conformational transition upon forming a complex with a steroid ligand. The CD and ORD spectra cannot be interpreted in terms of tertiary structure probably due to carbohydrate contributions. However, the difference spectra indicate strong perturbation of both a tryptophan residue and the steroid chromophore in the complex.
mesh_terms: D000818:Animals; D001665:Binding Sites; D002848:Chromatography, DEAE-Cellulose; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D002942:Circular Dichroism; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006168:Guinea Pigs; D009905:Optical Rotatory Dispersion; D011247:Pregnancy; D011374:Progesterone / Q000097:blood; D011485:Protein Binding; D011487:Protein Conformation; D011956:Receptors, Cell Surface; D012712:Serum Globulins / Q000302:isolation & purification; D013056:Spectrophotometry, Ultraviolet
chemical_list: D011956:Receptors, Cell Surface; D012712:Serum Globulins; D011374:Progesterone