A stereochemical model of the transpeptidation complex

Molecular models are proposed to describe the relative arrangement of aminoacyl and peptidyl tRNAs when bound to their respective A and P sites on the ribosome. The crystallographically determined structures of tRNAasp and tRNAphe have served as the models for these bound structures, while the imposed steric constraints for the model complexes were based on the results of published experimental data. The constructed models satisfy the stereochemical requirements needed for codon-anticodon interaction and for peptide bond formation. In this paper, the results of the complex containing tRNAphe as the A and P site bound transfer RNAs, is compared to a similarly constructed model which uses tRNAasp as the ribosome-bound transfer RNAs. The models have the following three major features: 1) the aminoacyl and peptidyl transfer RNAs assume an angle of approximately 45 degrees relative to each other; 2) in providing the proper stereochemistry for peptide bond condensation, a significant kink must be present in the messenger RNA between the A site and P site codons; and 3) a comparison of the two model complexes indicates that structural variations between the tRNAs or any allosteric transitions of the transfer RNAs associated with codon-anticodon recognition may be accommodated in the model by way of freedom of rotation about the phosphate backbone bonds in the mRNA between consecutive codons.     

Fragmentation of mitochondrial H+-ATPase hydrophobic complex]

The subunits with molecular weights of 30 000, 10 000 and 20 000 + 19 000 have been obtained by fractionation of the hydrophobic part of the oligomycin-sensitive ATPase complex on Sephadex G-200 and Sephadex G-150 in the presence of sodium dodecyl sulfate.     

Bioinorganic study on [Fe(promethazine)2H2O Cl]2+ complex

The coordination chemistry of iron (III) is the environment of an antihistaminic drug, promethazine has been explained to include a low spin, six-coordinate complex [Fe(Prometha)2(H2O) Cl] Cl2. Metaldrug interaction in vitro in aqueous KCl phase was studied polarographically at physiological pH and temperature. On the basis of elemental, magnetic, conductometric, IR, UV-visible, NMR spectroscopic analysis it is concluded that in solid phase two promethazine molecules with their N,N donor sites encompass the metal. Mass spectral study on the complex confirms that one of the three chlorides is involved in the coordination. The respective changes in the antihistaminic activity of the drug as a result of complexation has been determined and a possible mechanism is suggested.     

A family of double helices of alternating poly(gamma-benzyl-D-L-glutamate), a stereochemical model for gramicidin A.

Poly(γ-benzyl-d-l-glutamate) with strict alternation of l and d residues is found to exist, in addition to the α_DL and π_DL^4.4 helical structures already described (Heitz et al., 1975a), in four more helical structures. Models based on double helices made of antiparallel strands are proposed for all four structures, based on infrared, X-ray and electron diffraction data. These double helices are, like the single-stranded π_DL helices, specific to polypeptides with a strict stereosequence of alternating l and d residues. The diameter of the helical core of three of these helices appears to depend on the dimensions of the solvent molecules. Conformational angles (located in the β regions) and atomic co-ordinates determined by conformational energy analysis are given for the four structures. Experimental conditions used to obtain these helices, and to induce transconformations between the various helical structures of PBd-lG are described. The present investigations on PBd-lG help to make more precise the structure and geometry of models proposed (Veatch et al., 1974) for the antibiotic gramicidin A.     

Differentiation of [H]phencyclidine and ( + )-[H]SKF-10,047 binding sites in rat cerebral cortex

The potency of a series of opioid and non-opioid psychotomimetic drugs to inhibit the specific binding of [³H]PCP and ( + )-[³H]SKF-10,047 to rat cerebral cortical membranes was examined. ( + )-PCMP, the 3-methylpiperidino analog of PCP, was a potent inhibitor of the specific binding of both ligands. All of the other 12 compounds examined, however, displayed a 3-277-fold selectivity for either [³H]PCP or (+)-[³H]SKF-10,047 binding. These results suggest that although these opioid and non-opioid psychotomimetics bind to both sites, most have significantly different affinities. The binding sites for [³H]PCP appear to be distinct from the ‘sigma’ binding sites labeled with (+)-[³H]SKF-10,047.

SKF-10,047 Sigma receptor Phencyclidine Phencyclidine receptor Psychotomimetic activity     

[17(20)E]- and [17(20)Z]-pregna-5,17(20)-dien-21-oylamides. Facile synthesis and primary evaluation for cancer cells proliferation

Reaction of 17α-bromo-21-iodo-3β-acetoxypregn-5-en-20-one with ammonia, primary, and secondary amines is simple and convenient method for preparation of [17(20)E]- and [17(20)Z]-pregna-5,17(20)-dien-21-oylamides. Synthesis and characteristics of 12 related amides are presented. Primary testing on cells proliferation indicated differing effects of synthesized compounds on androgen insensitive MCF-7 cells and androgen sensitive LNCaP cells.     

AtCYP20-2 is an auxiliary protein of the chloroplast NAD(P)H dehydrogenase complex

AtCYP20-2 is one of 16 immunophilins in thylakoid lumen. The presence of the isomerase domain in AtCYP20-2, an enrichment of AtCYP20-2 in the stroma membranes and it’s co-migration with NAD(P)H dehydrogenase (NDH) in native gels provide evidence that AtCYP20-2 is an auxiliary protein of NDH. When different NDH mutants were studied, AtCYP20-2 was found to be strongly reduced especially in mutants deficient in the membrane domain of NDH, thus suggesting a role in the assembly of NDH hydrophobic domain. Lack of AtCYP20-2, however, did not lead to severe malfunction of NDH, indicating redundancy in the function of lumenal immunophilins.     

Conformations of Gly(n)H+ and Ala(n)H+ peptides in the gas phase

High-resolution ion mobility measurements and molecular dynamics simulations have been used to probe the conformations of protonated polyglycine and polyalanine (Gly(n)H and Ala(n)H+, n = 3-20) in the gas phase. The measured collision integrals for both the polyglycine and the polyalanine peptides are consistent with a self-solvated globule conformation, where the peptide chain wraps around and solvates the charge located on the terminal amine. The conformations of the small peptides are governed entirely by self-solvation, whereas the larger ones have additional backbone hydrogen bonds. Helical conformations, which are stable for neutral Alan peptides, were not observed in the experiments. Molecular dynamics simulations for Ala(n)H+ peptides suggest that the charge destabilizes the helix, although several of the low energy conformations found in the simulations for the larger Ala(n)H+ peptides have small helical regions.     

Lability of coupling between proton translocase and ATPase of mitochondrial H+-ATPase complex]

The interrelationship between the ATPase and H+-translocase functions of mitochondrial H+-ATPase was studied. The efficiency of the functioning was estimated by the value of coupling coefficient (Kc), which is represented by a ratio of proton translocation rate versus ATP coupling hydrolysis rate. It was shown that under conditions of increased concentrations of ATP and low concentrations of oligomycin the value of Kc is decreased. The increase in the concentration of valinomycin results in an increase of Kc. It was also found that the H+-ATPase activity shows a considerable increase during incubation of mitochondria, reaching its maximum with respect to both functions 1--2 min after addition of ATP. The data obtained are indicative of a lack of tight coupling between the H+-translocase and ATPase functions of mitochondrial H+-ATPase. The mechanism of action of H+-ATPase is discussed.     

Effect of Photoperiod on Metabolism of [H] Gibberellins A(1), 3-epi-A(1), and A(20) in Agrostemma githago L

To determine whether daylength influences the rate of metabolism of gibberellins (GAs) in the long-day (LD) rosette plant Agrostemma githago L., [³H]GA₂₀ and [³H]GA₁ were applied under short day (SD) and LD. Both were metabolized faster under LD than under SD. [³H]GA₂₀ was metabolized to a compound chromatographically identical to 3-epi-GA₁. [³H]GA₁ was metabolized to two acidic compounds, the major metabolite having chromatographic properties similar to, but not identical with GA₈. [³H]3-epi-GA₁ applied to plants under LD was metabolized much more slowly than was [³H]GA₁, and formed a very polar metabolite which did not partition into ethyl acetate at pH 2.5. Very polar metabolites were also formed after the feeds of [³H]GA₂₀ and [³H]GA₁. It was not possible to characterize these very polar compounds further because of their apparent instability. The results obtained suggest that in Agrostemma GA₂₀ is the precursor of 3-epi-GA₁, but there is at present no evidence indicating the precursor of GA₁.     

Four-site four-electron model for Bi(III)-Bi(V) mixed valence complex

In most quantum models for the four-site four-electron problem the lowest singlet state has two short and two long bonds in the absence of lattice polarization and is called the resonating valence bond (VB) state. It is shown here that if the lattice polarization is large, the ground state is a ‘negative U’ state with valence disproportionation (for example BaBiO₃ with Bi(V) and Bi(III) sites). Furthermore the model shows that the coupling between the pairs on different sites is provided via the VB state.     

DNA interactions of a functionalized ruthenium(II) mixed-polypyridyl complex [Ru(bpy)2ppd]2+

A novel polypyridyl ligand pteridino[7,6-f][1,10]phenanthroline-1,13(10H,12H)-dione (ppd) and its ruthenium(II) complex [Ru(bpy)2ppd]2+ have been synthesized and characterized by elemental analysis, electrospray mass spectra and 1H NMR. The interaction of the complex with calf thymus DNA was investigated by spectroscopic and viscosity measurements. The results suggest that the complex binds to DNA via an intercalative mode and serves as a molecular "light switch" for DNA. Moreover, the complex has been found to promote the photocleavage of plasmid DNA pBR322 under irradiation at 365 nm. The mechanism studies reveal that singlet oxygen (1O2) and superoxide anion radical (O2*(-))play a significant role in the photocleavage.     

Structural variety and stereochemical features of bis(diphenylphosphinyl)[3]ferrocenophane gold(I) complexes

The P,N-[3]ferrocenophane ligand 3 forms a (κP-ligand)AuCl complex (5) upon treatment with (Me₂S)AuCl. The corresponding P,P-[3]ferrocenophane system 4 yields a binuclear (κP,κP-chelate ligand)(AuCl)₂ complex (6) when reacted with 2 equivalents of the (Me₂S)AuCl reagent. Complex 6 features an intramolecular aurophilic Au?Au interaction. Treatment of the P,P-[3]ferrocenophane 4 with 1.0 equiv. of (PPh₃)AuCl gives the tetra-coordinated mono-gold(I) complex (P,P-ligand)(PPh₃)AuCl (7), whereas the cationic [(P,P-ligand)₂Au]⁺[Cl⁻] system is obtained from 4 and 0.5 equivalents of (Me₂S)AuCl. The [(P,P-ligand)₂Au]⁺ system is obtained in different diastereoisomeric forms (8 and 9) depending on the stereochemistry of the pair of P,P-[3]ferrocenophane chelate ligand used. Examples of the complexes 5, 6, 7 and 8 were characterized by X-ray diffraction.     

Vernalization and Gibberellin Physiology of Winter Canola (Endogenous Gibberellin (GA) Content and Metabolism of [3H]GA1 and [3H]GA20

Winter canola (Brassica napus cv Crystal) is an oilseed crop that requires vernalization (chilling treatment) for the induction of stem elongation and flowering. To investigate the role of gibberellins (GAs) in vernalization-induced events, endogenous GA content and the metabolism of [3H]GAs were examined in 10-week vernalized and nonvernalized plants. Shoot tips were harvested 0, 8, and 18 d postvernalization (DPV), and GAs were purified and quantified using 2H2-internal standards and gas chromatography-selected ion monitoring. Concentrations of GA1, GA3, GA8, GA19, and GA20 were 3.1-, 2.3-, 7.8-, 12.0-, and 24.5-fold higher, respectively, in the vernalized plants at the end of the vernalization treatment (0 DPV) relative to the nonvernalized plants. Thermoregulation apparently occurs prior to GA19 biosynthesis, since vernalization elevated the concentration of all of the monitored GAs. [3H]GA20 or [3H]GA1 was applied to the shoot tips of vernalized and nonvernalized plants, and after 24 h, plants were harvested at 6, 12, and 15 DPV. Following high-performance liquid chromatography analyses, vernalized plants showed increased conversion of [3H]GA20 to a [3H]GA1-like metabolite and reduced conversion of [3H]GA1 or [3H]GA20 to polar 3H-metabolites, putative glucosyl conjugates. These results demonstrate that vernalization influences GA content and GA metabolism, with GAs serving as probable regulatory intermediaries between chilling treatment and subsequent stem growth.     

Effect of Abscisic Acid on Uptake and Metabolism of [H]Gibberellin A(1) and [H]Pseudogibberellin A(1) by Barley Half-seeds

Uptake and metabolism of 1,2-[³H]gibberellin A₁ ([³H]GA₁, I) and its 3-hydroxy epimer ([³H]pseudoGA₁, II) by barley (Hordeum vulgare L.) half-seeds were measured after 24 hours of incubation, in the presence or absence of abscisic acid in the media. Uptake of both compounds was enhanced by abscisic acid, and abscisic acid enhanced the extent of metabolism of [³H]GA₁. However, [³H]pseudoGA₁ was not metabolized, even in the presence of abscisic acid. The significance of the stereo-chemistry of the 3-hydroxyl position is discussed.     

1H, (13)C, and (15)N NMR stereochemical study of cis-fused 7a(8a)-methyl and 6-phenyl octa(hexa)hydrocyclopenta[d][1,3]oxazines and [3,1]benzoxazines

Four 7a-methyl octa(or hexa)hydrocyclopenta[d][1,3]oxazines, five 8a-methyl octa(or hexa)hydro[3,1]benzoxazines, two 6-phenyl hexahydro[3,1]benzoxazinones, and 8a-methyl hexahydro[1,3]benzoxazinone, all cis-fused, were prepared and their stereostructures studied by various one- and two-dimensional (1)H, (13)C, and (15)N NMR spectroscopic methods. In solution, the cyclopentane-fused 2-oxo derivatives and the 1,3-benzoxazinone were found to attain exclusively the N-in/O-in conformation, whereas the 6-phenyl 2-oxo/thioxo derivatives were found to be present predominantly in the N-out conformation. The C-2 unsubstituted and the 2-oxo/thioxo 7a/8a-methyl derivatives were all present in solution as a rapidly interconverting equilibrium of the N-in and N-out conformations. The C-2 methyl derivatives were each found to be interconvertable mixtures of epimers (at C-2) with the N-in conformer predominating for one epimer and the N-out conformer predominating for the other, with both predominating conformers having the C-2 methyl group equatorially orientated. The substituent on the nitrogen (H or Me) was found to be always predominantly equatorial with respect to the heteroring, except for the epimeric 2-methyl derivatives with N-out conformations where steric constraints and the generalized anomeric effect resulted in the axial orientation of the C-2 methyl being favored.     

Chirality and stereochemical recognition in DNA-phytohormone interactions: A model approach

Space-filling molecular models of selected phytohormones and DNA, employed as described herein, illustrate possiblein vivo stereochemical recognition between nucleic acids and intercalated phytohormones. In this regard, the absolute chirality of certain phytohormones, and that of DNA may be essential for the recognition process. It is speculated further that the specific interactions shown by molecular models have significance in the evolution of plant regulatory mechanisms.     

H+ transport by reconstituted gastric (H+ + K+)-ATPase

Gastric (H+ + K+)-ATPase was reconstituted into artificial phosphatidylcholine/cholesterol liposomes by means of a freeze-thaw-sonication technique. Upon addition of MgATP, active H+ transport was observed, with a maximal rate of 2.1 mumol X mg-1 X min-1, requiring the presence of 100 mM K+ at the intravesicular site. However, in the absence of ATP an H+-K+ exchange with a maximal rate of 0.12 mumol X mg-1 X min-1 was measured, which could be inhibited by the well-known ATPase inhibitors vanadate and omeprazole, giving the first evidence of a passive K+-H+ exchange function of gastric (H+ + K+)-ATPase. An Na+-H+ exchange activity was also measured, which was fully inhibited by 1 mM amiloride. Simultaneous reconstitution of Na+/H+ antiport and (H+ + K+)-ATPase could explain why reconstituted ATPase appeared less cation-specific than the native enzyme (Rabon, E.C., Gunther, R.B., Soumarmon, A., Bassilian, B., Lewin, M.J.M. and Sachs, G. (1985) J. Biol. Chem. 260, 10200-10212).