[Pentacyclic steroid analogs: interaction of 16 alpha,17 alpha-cyclopentanoprogesterone with rat uterus proteins].
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.
Smirnov
A N
AN
Moscow State University, Biology Faculty, Russia. smirnov_an@hotmail.com
Pokrovskaia
E V
EV
Shevchenko
V P
VP
Levina
I S
IS
Kamernitskiĭ
A V
AV
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*
C113166:16,17-cyclopropanoprogesterone; D009124:Muscle Proteins; D014316:Tritium; D011374:Progesterone