Endocrinology, Vol 117, 1521-1529, Copyright © 1985 by Endocrine Society

ARTICLES

Identification of androgen-binding protein from testis cytosol and sertoli cell culture medium of the cynomolgus monkey, Macaca fascicularis

HS Keeping, SJ Winters and P Troen

The biochemical and immunological properties of monkey androgen-binding protein (mABP) from the cynomolgus monkey, Macaca fascicularis, have been examined in testis cytosol and medium of primary Sertoli cell- enriched cultures. mABP in testis tissue was separated from the serum protein testosterone-estradiol-binding globulin (mTeBG) by affinity chromatography on Concanavalin A-Sepharose (Con A). mTeBG from serum extracts was completely retained by the lectin and could be displaced with buffer containing alpha-methyl-D-glucoside. In contrast, mABP from testis extracts either did not interact with the Con A and appeared in the void volume or was partially retained by the column and could be eluted with buffer alone. A third component retained by the Con A may represent mTeBG contamination, a form of mABP which binds to Con A, or both. The specific 5 alpha-dihydrotestosterone (DHT)-binding activity in the void volume of the Con A column was designated mABP and was further studied. [3H]DHT binding to mABP was saturable and of limited capacity (0.163 +/- 19 pmol/mg protein). Scatchard analysis of the data was consistent with a single class of binding sites with an apparent dissociation constant (Kd) at 4 C of 2.6 +/- 0.2 X 10(-9) M. DHT was the most effective competitor of [3H]DHT binding to mABP, followed by 2- methoxyestradiol, testosterone, estradiol, and cyproterone acetate. Concentrated Sertoli cell culture medium subjected to steady state polyacrylamide gel electrophoresis produced a single peak of specifically bound [3H]DHT with a mobility similar to that of other androgen-binding proteins. [35S]Methionine-labeled medium proteins were immunoprecipitated with a rabbit anti-human TeBG antiserum. Two bands, corresponding to mol wt of approximately 46,000 and 48,000, were observed by fluorography, with the lighter component being more intense. After androgen affinity chromatography of radiolabeled medium proteins, these two bands were again observed on sodium dodecyl sulfate- urea-containing polyacrylamide gels. These results demonstrate that 1) mABP may be separated from mTeBG by lectin affinity chromatography, as in humans; 2) hTeBG and mABP are antigenically related; and 3) mABP consists of subunits of different mol wt in unequal ratios.