BIOSYNTHESIS OF A PUTATIVE GONADOTROPIN RECEPTOR COMPONENT BY RAT LEYDIG CELLS: ISOLATION OF A RADIOLABELED ACIDIC PROTEIN OF 79,000 MOLECULAR WEIGHT BY AFFINITY CHROMATOGRAPHY

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Abstract
The Leydig cells of the testis are known to possess high affinity receptors for luteinizing hormone and human chorionic gonadotropin (hCG), but no information concerning the synthesis of these receptors is available yet. In order to investigate this question, we have purified crude rat interstitial cell preparations on discontinuous Percoll gradients, and Leydig cells recovered from fractions demonstrating maximum testosterone production and hCG binding capacity were incubated for 17 h in a culture medium containing [35s]methionine. Radioactive proteins solubilized with Triton χ–100 were submitted to affinity chromatography on a resin consisting of hCG covalently linked to agarose. Proteins bound to the column were analyzed by two-dimensional gel electrophoresis. Autoradiography of the gel revealed a major protein (molecular weight: 79,000; pi 4.5) whose binding to the resin could be greatly diminished by an excess of hCG. The electrophoretic properties of this protein are similar to those of previously isolated gonadotropin receptor components.