DURING multiple passages, fibroblast cell lines retain the chromosome number and genetic defects of the original donor1,2. Here we show, by comparing the modes of glycolysis in foetal and non-foetal skin cultures, that-fibroblasts retain the expression of their original developmental state. illustration
CARBONIC anhydrase catalyses hydration of aldehydes1–3: illustration I have studied the relevance of hydration of glyceraldehyde-3-phosphate (GAP) in its oxidation by GAP dehydrogenase. GAP dehydrogenase activity was assayed spectrophotometrically by measuring the increase in absorbance at 340 nM of a reaction mixture containing 0.1 M Tris-HCl (pH 8.5), 17 mM sodium arsenate, 5 mM cysteine, 20 mM NaF, 1 mM NAD, 0.1 U/ml. of GAP dehydrogenase (Sigma) and 4 µM GAP.
IT has been shown that rabbit anti-serum against rat serum (RARS) injected intravenously into rats produces fatal anaphylactic shock1. This was interpreted as a reaction of RARS with γ-globulins adsorbed on the cell surface2. It therefore seemed reasonable to investigate the same effect on enhancing antibodies by injecting RARS into rats bearing Yoshida ascites sarcoma (YAS). The result was as expected–delayed death. It has been suggested that the “de-enhanced” tumour cells become more susceptible to lymphocytes3. Although the presence of enhancing antibodies coating YAS cells has not actually been shown, if they are responsible for the observed phenomena, other agents acting on γ-globulins should result in both anaphylaxis and “de-enhancement”. We therefore used cathepsins isolated from white blood cells, which act specifically on β and γ-globulins4. illustration
IT has been reported1 that washed human platelets incubated with 14C-labelled cytidine monophpsphate-N-acetyl sialic acid (CMP-NANA) in the presence of homogenized rat liver as the source of sialyltransferase showed an increase in the amount of sialic acid bound to the platelet membrane: illustration
REDUCED glutathione (GHS) is maintained in substantial concentration (3 × 10?3 M) within neurones1. The availability of new thiol-oxidizing agents like diamide2,3, which freely enter cells and the principal action of which is to reduce the GSH concentration by conversion to GSSG (equation 1), promoted an investigation of the effects of these agents on release of transmitter at frog myoneural junctions. illustration
ATMOSPHERIC oxygen is not in equilibrium with sea water with respect to the isotope exchange illustration but has an 18O excess of about 22‰ compared to sea water1. This could be due to isotope fractionation during respiration2. Another large contribution to the effect has been overlooked up to now. Photosynthesis on land takes place in transpiring leaves, where the difference in the vapour pressure of 16OH2 and 18OH2 concentrates the heavy molecules in their stationary water content. Since the free oxygen stems from the water in which photosynthesis takes place3–8 (with only a very small shift in isotopic composition9), photosynthesis on land is an 18O source for atmospheric O2. We have begun to study this effect quantitatively.
THE carboxy-terminal tetrapeptide of gastrin, Trp-Met-Asp-Phe-NH2, has the same biological activity as the parent hormone1. Morley2,3 showed that certain substitutions in the Trp, Met and Phe positions gave active analogues and concluded that these positions are concerned only with binding at the site of action. In contrast, the only substitution in aspartic acid that gave activity was tetrazolyl for the β-carboxyl, thereby maintaining a proton donor of similar size at this position. Morley concluded that the aspartyl residue has a functional rather than a binding role and presumably is indispensable. The carboxy-terminal octapeptide of cholecystokinin (OP-CCK) contains the carboxy-terminal tetrapeptide of gastrin and has gastrin-like activity4. We report here that the synthetic analogue of OP-CCK, in which alanyl is substituted for aspartyl at the position in question illustration, stimulates gastric acid secretion. In conscious cats with gastric fistulas5, dose-response curves were established for gastric acid response to OP-CCK, 7-Ala OP-CCK and pentagastrin6. The peptides were given by continuous intravenous infusion and response is taken as peak 10 min output during a 30 min infusion at each dose level (Fig. 1). Assigning a potency of 1 to OP-CCK the relative molar potency of 7-Ala OP-CCK is about 1/110 and of pentagastrin is about 1/4. We also tested the analogue of gastrin tetrapeptide in which alanyl is substituted for aspartyl illustration and found no detectable stimulation of acid secretion at doses as high as 15 mg/kg h, confirming similar negative findings by Morley2 in rat. This suggests that the weak action of alanyl substituted analogues cannot readily be detected without the enhancement of potency conferred by the sulphated tyrosyl of OP-CCK7. Ondetti et al.7 showed that 7-Ala OP-CCK contracts guinea-pig gallbladder with a potency about 1/150th that of OP-CCK, comparable with that reported here for acid secretion. This suggests that the same part or parts of the molecule are required for cholecystokinetic action and for gastric secretory action; the aspartyl residue in the penultimate position is dispensable for both of these actions. On the assumption that gastrin and CCK act at the same site8, we propose that the corresponding aspartyl residue of gastrin is similarly dispensable. For a direct test of this hypothesis, studies are needed of the synthetic analogue in which alanyl is substituted for the penultimate aspartyl in gastrin hepta-decapeptide, perferably gastrin II with sulphated tyrosyl because it is more potent than gastrin I in certain species9.
THE ribonuclease, barnase, produced by Bacillus amyloliquefaciens has a molecular weight of 12,382, consisting of 110 amino-acid residues. It is one of the smallest proteins containing neither disulphide bonds nor non-peptide cross-Bnks which nevertheless maintain a well defined tertiary structure1,2. The next smallest reported enzyme of similar nature is the lysozyme of phage T4, with 160 residues. The barnase structure is reversibly destroyed by denaturing solvents or heat2, in what approximates a one step, highly cooperative, transition. Studies of this reaction should be very useful in illustration approaching the general problem of sequence-determined folding in proteins. In particular, thermodynamically meaningful quantitative differences in the stability of various genetic variants and chemically modified, or synthetic, barnases could be measured. Some work has been reported on the effect of various environmental parameters on the transition3 as well as the effects of modification by carboxypeptidases4. Full utilization of such data requires knowledge of both amino-acid sequence and three dimensional structurs. The complete amino-acid sequence is reported here (Fig. 1). The sequence was obtained by conventional procedures involving analysis of peptides isolated after hydrolysis of the native or modified protein by various proteases.
THE molecular mechanism for initiating DNA replication can be studied using a subcellular system. Rao and Johnson1 found that HeLa cells in the pre-DNA-synthetic (G-1) period of the cell cycle initiate DNA synthesis after fusion with cells that are in the DNA synthetic (S) period. A previous subcellular system of DNA replication from HeLa cells2–4 consisted of intact nuclei, supplemented with the four deoxy-nucleoside triphosphates, salt, ATP and a cytosol factor. The nuclei in this system appeared to be permeable to proteins and DNA synthesis was very similar to that within intact cells. We report here the initiation of DNA synthesis in nuclei isolated from HeLa cells. Our results suggest that, with the synchronization method used, a small percentage of dormant G-1 nuclei can be stimulated by S-phase cytoplasm; this would be the case if the cells were receptive to stimulation for only 30–60 min during the cell cycle. illustration
A topological analysis based on density functional electronic and spin densities of the bonding characteristics in a series of Fe, Ru, Os, Tc and Rh dimers and trimers bridged, respectively, by μ-1,8-naphthyridine (nap) and μ-2,2′-dipyridylamine (dpa) is presented. By this simple qualitative analysis, we were able to determine the electronic ground state and correlated bonding order for a number of complexes potentially involved in extended metal atom chains (EMAC). Furthermore, we showed in the Ru dimer that it was possible to control the spin state simply by changing the bonded counter-anion.
High-level ab initio calculations on the complexes between noble gas atoms (He, Ne, Ar, Kr, and Xe) and dihalogen molecules (F2, Cl2, Br2, and I2) reveal trends, both in interaction energies and the energy difference between the linear and T-shaped structures, that can be explained well in terms of dispersion interactions enhanced by polar flattening of the halogens. The partial discrepancies with experimental findings are discussed.
A theoretical 1H NMR spectroscopy and thermodynamic analysis of the host–guest inclusion process involving the norfloxacin (NFX) into β-cyclodextrin (β-CD) was carried out. DFT structure and stabilization energies were obtained in both gas and aqueous phases. We could establish that the complex formation is enthalpy driven, and the hydrogen bonds established between NFX and β-CD play a major role in the complex stabilization. Besides, a theoretical 1H NMR analysis has shown to be a supplementary proceeding to predict appropriately the inclusion mode of norfloxacin molecule into the β-CD. In this work, a theoretical study of the NFX@β-CD complex is reported for the first time, seeking a deep understanding of topology and thermodynamics of the inclusion complex formation.
The 1A1 ground and the first 1B2 excited states of the methylenecyclopropene (triafulvene) are described by localized wave functions, based on 20 structures valence bond structures. The results are compared to CASSCF(4,4) calculations for both the energetics and the dipole moment. Additional calculations with partial electronic delocalization are presented, and it is shown that the dipole moment modification does not correspond to a situation where the antiaromatic situation prevails (with 4n electrons in the cycle). Part of the analysis uses a “trust factor” that helps to decide if a wave function is appropriate to describe a given state. The trust factor compares the VB wave function to the CASSCF’s with their overlap. Finally, the valence bond density is used to produce density maps that illustrate the electron transfer upon excitation.
Graphical Abstract A projector-based method compares CASSCF wave functions to local wave functions, including Lewis structures as shown in the picture. A “trust factor” (τ) is obtained. Both the ground state and the first excited state of the methylenecyclopropene are discussed
The present study reports the geometries, electronic structures, growth behavior, and stabilities of neutral and ionized copper-doped germanium clusters containing 1–20 Ge atoms within the framework of linear combination of atomic orbitals density functional theory (DFT) under the spin-polarized generalized gradient approximation. It was found that Cu-capped Gen (or Cu-substituted Gen+1) and Cu-encapsulated Gen clusters mostly occur in the ground state at a particular cluster size (n). In order to explain the relative stabilities of the ground-state clusters, parameters such as the average binding energy per atom (BE), the embedding energy (EE), and the fragmentation energy (FE) of the clusters were calculated, and the resulting values are discussed. To explain the chemical stabilities of the clusters, parameters such as the energy gap between the highest occupied and the lowest unoccupied molecular orbitals (the HOMO–LUMO gap), the ionization energy (IP), the electron affinity (EA), the chemical potential (μ), the chemical hardness (η), and the polarizability were calculated, and the resulting values are also discussed. Natural atomic orbital (NAO) and natural bond orbital (NBO) analyses were also used to determine the electron-counting rule that should be applied to the most stable Ge10Cu cluster. Finally, the relevance of the calculated results to the design of Ge-based superatoms is discussed.
Figure Contributions of the valance orbitals of the Ge and Cu atom(s) to the HOMO of the ground-state icosahedral Ge10Cu cluster obtained from NBO analysis. The numbers below the clusters represent the occupancies of the HOMO orbitals
A DNA enzyme with peroxidase activity is a G-quadruplex-based DNAzyme formed by hemin and G-quadruplex DNA. Activity of peroxide DNAzymes can be influenced by the structure of quadruplex DNA. In this investigation, the interaction of hemin with T30695 G-quadruplex DNA is evaluated. Molecular dynamic simulation indicates that the binding mode of hemin to G-quadruplex DNA is end-stacking, which is consistent with absorption spectroscopy. Based on fluorescence spectroscopy, hemin ejects thiazole orange from bases of four-strand DNA. Circular dichroism spectra showed that no alteration occurs in this type of DNA structure.
In this work, through a docking analysis of compounds from the ZINC chemical library on human β-tubulin using high performance computer cluster, we report new polycyclic aromatic compounds that bind with high energy on the colchicine binding site of β-tubulin, suggesting three new key amino acids. However, molecular dynamic analysis showed low stability in the interaction between ligand and receptor. Results were confirmed experimentally in in vitro and in vivo models that suggest that molecular dynamics simulation is the best option to find new potential β-tubulin inhibitors.
The adsorption of 20 amino acids (AAs) on the (101) surface of anatase titanium dioxide (TiO2) has been investigated under the scheme of density functional theory. Through the analysis of adsorption geometries, amino group and side chains of AAs have been identified as the major side to adsorb on TiO2, while the carboxyl group prefers to stay outside to avoid the repulsion between negatively charged oxygen from TiO2 and AAs. On the surface, two-coordinated oxygen is the major site to stabilize AAs through O–H interactions. The above conclusion does not change when it is in the aqueous solution based on the calculations with AAs surrounded by explicit water molecules. The above knowledge is helpful in predicting how AAs and even peptides adsorb on inorganic materials.
Graphical abstract The adsorption of 20 amino acids (AAs) on the (101) surface of anatase titanium dioxide (TiO2) has been investigated under the scheme of density functional theory.
