title: Interactions of 16alpha,17alpha-cyclohexane derivatives of progesterone with the progesterone receptor from rat uterus.
abstract: Pregna-D'-pentaranes, 16alpha,17alpha-cyclohexanoprogesterone and 6alpha-methyl-16alpha,17alpha-cyclohexanoprogestero ne, were found to specifically interact with the progesterone receptor of soluble fraction from rat uterus. The formation of complexes between 3H-labeled derivatives of these steroids and the protein was complete within 1 to 3 h at 0-4 degreesC. The dissociation of these complexes was a two-phase process, the contribution of the fast dissociating complexes decreasing with increasing preincubation time. The dissociation constant (k-1) values for progesterone, 16alpha, 17alpha-cyclohexanoprogesterone, and 6alpha-methyl-16alpha, 17alpha-cyclohexanoprogesterone complexes with the protein after 1 h preincubation were 6.5 +/- 0.8, 8.8 +/- 5.5, and (16.6 +/- 5.6).10(-4) sec(-1) for the fast phase and 5.1 +/- 0.5, 3.5 +/- 0.8, and (2.8 +/- 0.6).10(-5) sec(-1) for slow phase, respectively. The equilibrium Kd values were 11.7 +/- 2.1, 19.0 +/- 2.0, and 66.1 +/- 14.6 nM for progesterone, 16alpha,17alpha-cyclohexanoprogesterone, and 6alpha-methyl-16alpha,17alpha-cyclohexanoprogestero ne, respectively. The steroids mutually inhibited the binding of their 3H-labeled derivatives to the protein, the inhibition being of competitive type. In the case of [3H]6alpha-methyl-16alpha, 17alpha-cyclohexanoprogesterone, the inhibitory efficacy of progesterone declined with an increase of its concentration; this points to possible heterogeneity of binding sites for the 3H-labeled ligand. The comparison of the results with those obtained by us earlier (Biochemistry (Moscow), 1996, 61, 1034-1041) suggests the existence of significant species differences in progesterone receptor structure within or near the region that interacts with the D-ring of a hormone molecule.
authors.affiliation: Laboratory of Endocrinology, School of Biology, Lomonosov Moscow State University, Moscow, 119899, Russia.
authors.forename: A N
authors.initials: AN
authors.lastname: Smirnov
authors.forename: E V
authors.initials: EV
authors.lastname: Pokrovskaya
authors.forename: V P
authors.initials: VP
authors.lastname: Shevchenko
authors.forename: I S
authors.initials: IS
authors.lastname: Levina
authors.forename: A V
authors.initials: AV
authors.lastname: Kamernitzky
mesh_terms: D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D005260:Female; D066298:In Vitro Techniques; D007700:Kinetics; D011374:Progesterone / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D051381:Rats; D011980:Receptors, Progesterone / Q000737:chemistry / Q000378:metabolism*; D014316:Tritium; D014599:Uterus / Q000378:metabolism*
chemical_list: D011980:Receptors, Progesterone; D014316:Tritium; C085261:pentarane A; D011374:Progesterone; C085262:pentarane B