Luteinizing hormone-receptor interaction in the testis: progressive decrease in reversibility of the hormone-receptor complex.

Abstract

The interaction of LH and other hormones with specific receptor sites is accompanied by a progressive change in the degree of reversibility of the hormone-receptor complex. This process was investigated by analysis of in vitro binding of [125]hCG to 15,000 × g fractions of rat testis homogenate. During the first hour of incubation at 37 C, dilution and washing of the particles gave about 20% less specific binding than when particles were incubated with excess unlabeled hormone for a further 1 h before dilution and washing. This effect was no longer demonstrable after 4 h, suggesting that the hormone-receptor complex became less reversible to dilution with time. A decrease in reversibility was also noted when hormone-receptor complexes formed by preincubation with [125I]hCG at 37 C were dissociated with MgCl2 at successive intervals after binding. Thus, 90% of the complexes formed in the first 10 min could be dissociated by 1 M MgCl2, whereas about 50% of the complexes was dissociable at 10–p20 min, and on...