title: [Pentacyclic steroid analogs: interaction of 16 alpha,17 alpha-cyclopentanoprogesterone with rat uterus proteins].
abstract: Using 3H-labeled derivatives, kinetic parameters of specific binding of progesterone (I) and 16 alpha, 17 alpha-cyclopentanoprogesterone (II) to proteins of the uterus soluble fraction in rats were measured. It was shown that their affinities to proteins are comparable (K 10.5 +/- 2.4 and 6.7 +/- 3.4 nM for (I) and (II), respectively, upon 22 h incubation). The unlabeled compound (II) can displace [3H]progesterone from complexes with the protein with a concentration-independent efficiency corresponding to the ratio of K values for compounds (I) and (II). At the same time, the efficiency of the unlabeled progesterone in the displacement of [3H]compound (II) from protein complexes fell with an increase in the progesterone concentration. The concentration of high-affinity sites of [3H]compound (II) exceeded by 1.5 to 2 times the concentration of sites for [3H]progesterone. Dynamics of dissociation of proteins complexes of [3H]progesterone and 3H]compound (II) had a two-phase character with a decrease in the dissociation rate constants for both phases as the times of exposition of [3H]ligands to proteins grew. The ratio of slow- and fast-dissociating ligand-receptor complexes was thereby unchanged. These data suggest the presence in the rat uterus soluble fraction of two types of proteins differing in the capacity to recognize the additional five-membered ring D' in the steroid molecule.
authors.affiliation: Moscow State University, Biology Faculty, Russia. smirnov_an@hotmail.com
authors.forename: A N
authors.initials: AN
authors.lastname: Smirnov
authors.forename: E V
authors.initials: EV
authors.lastname: Pokrovskaia
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: Kamernitskiĭ
mesh_terms: D000818:Animals; D005260:Female; D007700:Kinetics; D015394:Molecular Structure; D009124:Muscle Proteins / Q000378:metabolism*; D011374:Progesterone / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D051381:Rats; D014316:Tritium; D014599:Uterus / Q000378:metabolism*
chemical_list: C113166:16,17-cyclopropanoprogesterone; D009124:Muscle Proteins; D014316:Tritium; D011374:Progesterone