title: Purification and characterization of a membrane-associated testosterone-binding protein from Pseudomonas testosteroni.
abstract: A steroid-binding protein, identified in the supernatant generated when membrane vesicles of Pseudomonas testosteroni are produced and harvested by centrifugation, has been purified 49-fold to homogeneity. It has a molecular weight of 30 000-35 000 and it specifically binds the C19 steroids dihydrotestosterone, testosterone, and androstenedione. It is a basic protein with an isoelectric point at pH 7.3. Binding of testosterone exhibited normal saturation kinetics with an affinity constant, Kd, of 3.9 X 10(-8) M. Binding was inhibited by divalent cations, but the sulfhydryl reagents dithiothreitol and mercaptoethanol did not affect activity. It is suggested that this and other membrane-associated steroid-binding proteins concentrate the steroid at the membrane surface before it is transported into the cytoplasm of P. testosteroni.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000727:Androgen-Binding Protein / Q000302:isolation & purification / Q000378:metabolism*; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D007700:Kinetics; D008970:Molecular Weight; D011549:Pseudomonas / Q000378:metabolism*; D013739:Testosterone / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D000727:Androgen-Binding Protein; D002352:Carrier Proteins; D013739:Testosterone