title: The dissociation of testosterone- and 5 alpha-dihydrotestosterone-receptor complexes formed within cultured human genital skin fibroblasts.
abstract: We have studied the rate and character with which testosterone (T) and 5 alpha-dihydrotestosterone (DHT) dissociate from the androgen receptor both within intact cultured genital skin fibroblasts of a subject with 5 alpha-reductase deficiency and after the androgen-receptor complexes have been extracted from the cells. Within the cells, the kinetics of the dissociative process for each hormone was first-order, but T dissociated four times faster than DHT. An Arrhenius plot of the variation of the dissociation rate constants with temperature for T was linear and yielded an activation energy of 28 kcal/mol. This value is identical with the one previously determined for activated DHT-receptor complexes. T-receptor complexes extracted from the cells dissociated with complex kinetics: at 37 degrees C the rate constants of the "fast" and "slow" components were 40 and 14 X 10(-3) min-1, respectively. In contrast, DHT-receptor complexes extracted from the cells dissociated with first-order kinetics and at a rate identical to that observed within cells, except after exposure to pyridoxal 5'-phosphate (5 mM) or concentration by Amicon (B-15) filtration, when their dissociation kinetics became complex. We interpret these data to mean that, within the cells, both T- and DHT-receptor complexes exist predominantly in the activated state whereas, when extracted from the cells, DHT-receptor complexes remain activated, unless perturbed, while T-receptor complexes become unstable spontaneously, probably by reverting to a preactivated state.
mesh_terms: D002478:Cells, Cultured; D013196:Dihydrotestosterone / Q000378:metabolism*; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008297:Male; D010413:Penis; D011732:Pyridoxal Phosphate / Q000494:pharmacology; D011944:Receptors, Androgen / Q000187:drug effects / Q000378:metabolism*; D011987:Receptors, Steroid / Q000378:metabolism*; D012867:Skin / Q000378:metabolism*; D013739:Testosterone / Q000378:metabolism*; D013816:Thermodynamics; D014621:Vagina
chemical_list: D011944:Receptors, Androgen; D011987:Receptors, Steroid; D013196:Dihydrotestosterone; D013739:Testosterone; D011732:Pyridoxal Phosphate