Mock E J, Papkoff H, Niswender G D
Endocrinology. 1983 Jul;113(1):265-9. doi: 10.1210/endo-113-1-265.
The rate of internalization and degradation of radioiodinated hCG and ovine LH (oLH) as well as homologous and heterologous recombinants of their subunits was studied in suspensions of ovine luteal cells. Hormone bound to the plasma membrane was quantified by treating the cells with acidic buffer (pH 3.0) and quantification of the radioactivity that was removed from receptor. The radioactivity remaining in the cell pellet was considered to be intracellular. The extent of degradation of the radioactive hormones was determined by subjecting the radioactivity released into the medium during incubation to precipitation with 20% trichloroacetic acid. The non-precipitable radioactivity was considered to have been degraded. Radioactivity was lost from the cell membrane with a t1/2 of 16.8 +/- 2.5 h for radioiodinated hCG, 22.8 +/- 3.8 h for the alpha-subunit of hCG recombined with radioiodinated beta-subunit of hCG, 8.9 +/- 4.5 h for the alpha-subunit of oLH recombined with the radioiodinated beta-subunit of hCG, 0.5 +/- 0.1 h for the alpha-subunit of hCG recombined with the radioiodinated beta-subunit of oLH, 0.5 +/- 0.1 h for radioiodinated oLH, and 0.7 +/- 0.2 h for the alpha-subunit of oLH recombined with the radioiodinated beta-subunit of oLH. In general, the levels of radioactivity that were intracellular and the rate of degradation of the hormone were inversely related to the quantities of hormone that remained on the plasma membrane. The preparations that contained the beta-subunit of hCG were all internalized at a slower rate (t1/2 = 9-22 h) and consequently were degraded more slowly than any of the preparations that contained the beta-subunit of oLH (t1/2 = 0.5-0.7 h). When the radioiodine in oLH was present in the beta-subunit, intracellular levels of radioactivity were higher and degradation occurred more rapidly than when the radioiodine was in the alpha-subunit. Although the differences were less dramatic, hCG with radioiodine in the beta-subunit also reached higher levels intracellularly, but was degraded to a lesser extent at 16 and 24 h than was hCG with radioiodine in the alpha-subunit. These data demonstrated a dramatic difference (approximately 30-fold) in the rate of loss of oLH vs. that of hCG from the membrane of ovine luteal cells. Further, it appears that the beta-subunit of each of the two hormones is the major factor in determining the rate of internalization of the intact hormone. The differences is how the two hormones are processed at the receptor level may help explain the known differences in their steroidogenic potencies.
在绵羊黄体细胞悬液中研究了放射性碘化人绒毛膜促性腺激素（hCG）和绵羊促黄体生成素（oLH）及其亚基的同源和异源重组体的内化和降解速率。通过用酸性缓冲液（pH 3.0）处理细胞并对从受体上移除的放射性进行定量来测定结合到质膜上的激素。细胞沉淀中剩余的放射性被认为是细胞内的。通过对孵育期间释放到培养基中的放射性用20%三氯乙酸进行沉淀来确定放射性激素的降解程度。不可沉淀的放射性被认为已被降解。放射性从细胞膜上丢失的半衰期分别为：放射性碘化hCG为16.8±2.5小时，与放射性碘化hCGβ亚基重组的hCGα亚基为22.8±3.8小时，与放射性碘化hCGβ亚基重组的oLHα亚基为8.9±4.5小时，与放射性碘化oLHβ亚基重组的hCGα亚基为0.5±0.1小时，放射性碘化oLH为0.5±0.1小时，与放射性碘化oLHβ亚基重组的oLHα亚基为0.7±0.2小时。一般来说，细胞内的放射性水平和激素的降解速率与留在质膜上的激素量呈负相关。含有hCGβ亚基的制剂内化速率均较慢（半衰期=9 - 22小时），因此降解速度比任何含有oLHβ亚基的制剂（半衰期=0.5 - 0.7小时）都要慢。当oLH中的放射性碘存在于β亚基中时，细胞内放射性水平较高，且降解比放射性碘存在于α亚基中时更快。虽然差异不那么显著，但β亚基含有放射性碘的hCG在细胞内也达到较高水平，但在16小时和24小时时比α亚基含有放射性碘的hCG降解程度小。这些数据表明，oLH与hCG从绵羊黄体细胞质膜上丢失的速率存在显著差异（约30倍）。此外，似乎这两种激素的β亚基是决定完整激素内化速率的主要因素。两种激素在受体水平上的处理方式差异可能有助于解释它们已知的类固醇生成能力差异。
