SEX HORMONE BINDING PROTEINS .2. ISOLATION FROM SERUM OF AN ELASMOBRANCH (RAJA RADIATA)

A sex hormone binding protein (SHBP), homogeneous by polyacrylamide gel electrophoresis, was isolated from the serum of the mature male thorny skate (Raja radiata) by DEAE-cellulose chromatography and Sephadex G-200 gel filtration. The molecular weight of the protein as determined by Sephadex G-200 thin layer chromatography and Sephadex G-200 gel filtration was found to be about 80,000. The SHBP monomer is believed to associate into more complex molecules with a loss in steroid binding activity. Association was prevented and reversed to some extent by including 2-mercaptoethanol or dithiothreitol in buffers used in isolating the protein. A high binding affinity for testosterone was demonstrated by gel filtration. Under competitive binding conditions, the skate SHBP, like human testosterone binding globulin, had a greater binding affinity for 5α-androstane-3β,17β-diol than testosterone while epitestosterone with its 17α-configuration was not bound appreciably. Unlike what has been found for human testosterone binding globulin some compounds which possess a lateral chain at C-17 compete with testosterone for the SHBP. When testosterone binding to SHBP is rated at 100, the binding of estradiol-17β, progesterone, 17α-hydroxyprogesterone, and 1α-hydroxycorticosterone are rated at 125, 118, 108, and 2, respectively. © 1969.