Effect of mifepristone (RU 486) on concentrations of prostaglandin E-2 binding sites in the rat endometrium

Progesterone implants in ovariectomized rats increased endometrial concentrations of PGE-2 receptors. The increase was completely inhibited by simultaneous daily injection (7.5 mg/kg) of mifepristone (RU 486). A single injection of mifepristone on the morning of Day 1 of pseudopregnancy (day of oestrus) decreased the amount of PGE-2 receptors found in the endometrium on Day 5 by 64%. This inhibitory effect probably resulted from the antiprogesterone activity of this compound since it was not counteracted by simultaneous treatment with dexamethasone, shown to reverse totally the antiglucocorticoid action of mifepristone. The inhibition by mifepristone lasted only for 1 day; endometrial PGE-2 receptor levels on Day 6 of pseudopregnancy returned to the high values present in controls. Under these conditions, administration of the mifepristone did not affect the plasma oestradiol and progesterone concentrations during the 1st week of pseudopregnancy. The administration of mifepristone on Days 2 and 3 of pseudopregnancy kept the endometrial PGE-2 receptor levels low, even by 4 days after the end of treatment. We therefore concluded that, in the rat, progesterone priming leading to uterine receptivity can be delayed, at least by 1 day. In contrast, interruption of the progesterone action for a longer period later during the early pseudopregnant period resulted in an altered subsequent evolution of the endometrium, in terms of acquisition of the PGE-2 binding sites.     

An inquiry into the selective protection of glycine during the radiolysis of glycine-alanine mixtures in aqueous solutions and its implications to the preservation of optically active amino acids in the early earth

Akaboshi et al. (1990) has found an unexpected protection of the achiral amino acid, glycine, towards ionizing radiation at the expense of the selective destruction of the chiral amino acids, alanine and aspartic acid. The present work examines the mechanism of this protection for the case of alanine. We have developed a computer model for the radiolysis of glycine, alanine and glycine-alanine mixtures in aqueous solution. It is established that this protection is due in part to the reaction of the α-radical of glycine with alanine to regenerate a more stable α-radical, according to the following reaction, $$ \cdot CH(NH_3^ + )CO_2^ - + CH_3 CH(NH_3^ + )CO_2^ - \to CH_2 (NH_3^ + )CO_2^ - + CH_3 \dot C(NH_3^ + )CO_2^ -$$ The rate constant of this reaction was estimated to be ≤10⁴M^-1s^-1. The implications for this selective protection of glycine are considered for a hypothetical case in which there would be an enrichment of about 10% ofL-alanine in the primitive ocean and taking the glycine/alanine ratios obtained in CH₄-and CO₂- dominated atmospheres using electric discharge experiments. It is predicted that alanine would be rapidly destroyed and radioracemized in spite of the fact that the concentration of alanine is equal or significantly lower than that of glycine. Assuming that chiral amino acids were a prerequisite for the origin of life, it can be deduced that life could have appeared in a relatively short period of time unless there was a constant supply of optical amino acids from extraterrestrial sources.     

Lactam bridge stabilization of α-helical peptides: Ring size,orientation and positional effects

A series of 14 residue amphipathic α-helical peptides, in which the sidechains of glutamic acid and lysine have been covalently joined, was synthesized in order to determine the effect of spacing, position and orientation of these lactam bridges. It was found that although an (i, i+3) spacing would position the lactam bridge on the same face of the helix, these lactams with 18-member rings were actually helix-destabilizing regardless of position or location. On the other hand, (i, i+4) lactams with 21-member rings were helix-stabilizing but this was dependent on orientation. Glutamic acid-lysine lactams increased the helical content of the peptide when compared with their linear homologue in benign conditions (50 mM KH₂PO₄, 100 mM KCl, pH 7). Two Glu-Lys (i, i+4) lactams located at the N- and C-termini gave rise to a peptide with greater than 99% helical content in benign conditions. Peptides with Lys-Glu oriented lactams were random structures in benign conditions but in the presence of 50% TFE could be induced into a helical conformation. The stability of the single-stranded α-helices, as measured by thermal denaturations in 25% TFE indicated that Glu-Lys oriented lactam bridges stabilized the helical conformation relative to the linear unbridged peptide. One Glu-Lys lactam in the middle of the peptide was more effective at stabilizing helical structure than two Glu-Lys lactams positioned one at each end of the molecule. The lactams with the Lys-Glu orientation were destabilizing relative to the unbridged peptide. This study demonstrates that correct orientation and position of a lactam bridge is critical in order to design peptides with high helical content in aqueous media.     

Conformational differences between cis and trans proline isomers of a peptide antigen representing the receptor binding domain of Pseudomonas aeruginosa as studied by 1H-nmr

A 17-residue disulfide-bridged peptide (PAK 128–144) corresponding to the C-terminus of Pseudomonas aeruginosa pilin strain K has been studied by one- and two-dimensional nmr techniques. This synthetic immunogen has been found to exist as two distinct conformations in solution, which have been demonstrated to arise as a result of the isomerization of the I¹³⁸-P¹³⁹ amide bond. The two isomers occur in the ratio of 3 : 1 trans to cis at 5°C. Sequential assignments for both forms have been accomplished through the use of nuclear Overhauser enhancement spectroscopy (NOESY) spectra and most side-chain resonances have been assigned using a combination of correlated spectroscopy, total correlated spectroscopy, and NOESY spectra. The presence of the cis isomer, which is considerably more predominant in the oxidized peptide, was confirmed by the observation of the characteristic NOEs between P¹³⁹ and the preceding residue. Further corroboration was given by the disappearance of the cis resonances in the spectrum of the P139A analogue of PAK 128–144. From observation of the differences in the chemical shifts and amide proton temperature coefficients of the two isomers, it is apparent that the two forms differ markedly in their solution conformation. The biological implications of the isomerization are discussed. © 1994 John Wiley & Sons, Inc.     

Purification and Properties of Manganese Superoxide Dismutase from Norway Spruce (Picea abies L. Karst)

A manganese-containing superoxide dismutase (SOD; EC 1.15.1.1 [EC] )was purified to electrophoretic homogeneity from seeds of Norwayspruce (Picea abies L.). The apparent molecular mass of thepurified enzyme was 86 kDa, as determined by gel filtration.The subunit molecular mass, estimated by SDS-polyacrylamidegel electrophoresis, was 22 kDa both in the presence and inthe absence of 2-mercaptoethanol. Thus, the native enzyme isa homotetramer with subunits that were not linked by disulfidebonds. The isoelectric point of this Mn-SOD was 5.5. The specificactivity of the Mn-SOD was strongly pH-dependent and was 400units per nmol SOD at pH 7.8 and 30 units per nmol SOD at pH10.4. The first 25 amino acid residues in the amino terminalregion of spruce Mn-SOD exhibited a high degree of sequencehomology to those of Mn-SODs from other organisms. In Mn-deficientneedles the activity of Mn-SOD was only half of that in non-deficientneedles, whereas the activity of CuZn-SOD was doubled. (Received May 20, 1994; Accepted October 31, 1994)