Transverse dipoles added to DNA chains by drug binding can induce inversion of the long-range chirality of DNA condensates

The addition of poly(ethylene glycol) (PEG) to a DNA solution induces phase separation of droplets of condensed DNA. These droplets possess liquid crystalline properties and their ordering is cholesteric. It was recently proved that daunomycin, by binding to DNA chains, inverts the long-range chirality of their tertiary packing into aggregates. The present paper suggests one possible mechanism by which this inversion can take place. Daunomycin bears a cationic group in its sugar residue. Its intercalation adds a helicoidal distribution of transverse dipoles to DNA chains. By this mechanism, in favourable cases, ionic or strongly polar groups in drugs which bind DNA can induce handedness inversion of the cholesteric ordering of its condensates. This inversion mechanism was tested experimentally using several, charged and uncharged, homologues of daunomycin. All those bearing the cationic ammonium group inverted the long-range chirality of the PEG-induced DNA mesomorphic state. The effects of the uncharged desamino homologues could not be evaluated because of their lower solubility and binding affinity for DNA.     

Acetoacyl-acyl carrier protein synthase from avocado: its purification,characterisation and clear resolution from acetyl CoA:ACP transacylase

-ketoacyl-ACP synthetase III (KAS III) has been purified from avocado using a six-step purification procedure. The enzyme, which is cerulenin-insensitive and thiolactomycin-sensitive, was assayed using a partial component reaction: acetyl CoA:ACP transacylase (ACAT) activity. KAS III activity is distinguished from ACAT activity on the basis that the former is highly stimulated by the addition of malonyl CoA in the presence of malonyl-CoA:ACP transacylase, and the latter is not. KAS III and ACAT activity have been separated from each other thus providing the first evidence that these two discrete activities exist in higher plants. Both of these enzymes have been implicated in the initial reactions of fatty acid synthesis.KAS III was purified 134-fold using a combination of PEG precipitation, Fast Q, ammonium sulphate precipitation, Phenyl Sepharose and ACP-affinity chromatography. The enzyme requires Triton X-100 for solubility and is highly salt sensitive. The subunit molecular mass of 37 kDa has been identified by SDS-PAGE. The results of gel filtration analysis are consistent with the native enzyme being homodimeric. The native molecular mass of KAS III is 69 kDa and that of ACAT 18.5 kDa. The enzyme has a pH optimum of 7.0–7.5, which is similar to the pH optimum of the ACAT reaction. The Km for acetyl CoA is 12.5 M and the Km for malonyl-ACP is 14M. Both KAS III and ACAT are sensitive to thiolactomycin inhibition. The results are discussed with respect to the potential role of acetyl CoA:ACP transacylase in plants.     

The Apoptotic and Nonapoptotic Nature of the Terminal Differentiation of Erythroid Cells

The morphology of erythroid cells changes dramatically during the course of their terminal differentiation. According to calculations made with cytospin preparations obtained from Syrian hamster yolk-sac-derived erythroid cells, the area of nuclei at day 10 of gestation ranges from 25 to 85 μm²and is reduced to 15–25 μm²on day 13 [K. Morioka and R. Minamikawa-Tachino,Dev. Growth Differ.35, 569–582, 1993]. The DNA and protein contents of each nucleus also decrease during this period. Nonspecific fragmentation of DNA was detected by agarose gel electrophoresis in all samples obtained from day 10 to day 13 of gestation, while distinct ladders of DNA fragments were not detected. DNA fragmentation was also detected by anin situDNA-end labeling (TUNEL) assay. As the terminal differentiation proceeded, gradual decreases in levels of both histone H1 and most nonhistone proteins were observed by SDS–polyacrylamide gel electrophoresis, while levels of core histones appeared to be constant. In particular, lamin B₂was almost completely lost from the nuclear matrix fraction on day 11. These results suggest that the terminal differentiation of erythroid cells and apoptosis might have common mechanisms. However, expansion of the cytoplasm during the terminal differentiation distinguishes these processes. In addition, in the erythroid terminal differentiation, nuclei never form lobules or become fragmented; no apoptotic bodies are formed, occurrence of the apoptosis-like cellular change is not sporadic but rather synchronous, and the process is slow, with at least several days being required for cell death. These characteristics are different from those of typical apoptosis. Thus, the terminal differentiation of nucleated embryonic erythroid cells exhibits both apoptotic and nonapoptotic features.     

Mineral Catalysis of a Potentially Prebiotic Aldol Condensation

Minerals may have played a significant role in chemical evolution. In the course of investigating the chemistry of phosphonoacetaldehyde (PAL), an analogue of glycolaldehyde phosphate, we have observed a striking case of catalysis by the layered hydroxide mineral hydrotalcite ([Mg₂Al(OH)₆][Cl.nH₂O]). In neutral or moderately basic aqueous solutions, PAL is unreactive even at a concentration of 0.1 M. In the presence of a large excess of NaOH (2 M), the compound undergoes aldol condensation to produce a dimer containing a C3–C4 double-bond. In dilute neutral solutions and in the presence of the mineral, however, condensation takes place rapidly, to produce a dimer which is almost exclusively the C2–C3 unsaturated product. Received: 11 February 1998 / Accepted: 12 May 1998     

Clastogenic effects of bleomycin, cyclophosphamide, and ethyl methanesulfonate on resting and proliferating human B- and T-lymphocytes

The effects of bleomycin (BM), cyclophosphamide (CP), and ethyl methanesulfonate (EMS) on the frequencies of chromosomal aberrations were tested in mitogen-stimulated highly purified human B- and T-lymphocytes. In unstimulated G0/G1 B- and T-lymphocytes the clastogen induction of chromosome fragments was investigated in prematurely condensed chromosomes (PCC) induced by cell fusion with xenogenic mitotic cells. BM, CP (with metabolic activation), and EMS induced a significant increase in chromosome aberrations in proliferating human B- and T-lymphocytes. There were no significant differences in the BM-induced aberration rates between the cell populations. CP and EMS induced more aberrations in T- than in B-lymphocytes. In the PCC tests, BM-exposed G0/G1 lymphocytes showed dose-dependent high yields of chromosome fragments. No significant differences between B- and T-lymphocytes were observed. CP and EMS induced no clear increase in fragments in either cell population.     

Dispersal distances of the Caribbean fruit fly,corn planthopper and Cuban May beetle

Summary Adults of the Caribbean fruit fly,Anastrepha suspensa (Loew), and Cuban May beetle,Phyllophaga bruneri Chapin, were recovered at various distances from release sites. Corn planthopper,Peregrinus maidis (Ashmead), adults were numerous and more dead corn plants were found beside the grassy areas indicating that incidence of the disease was related to the insect abundance. Regression curves showed that rates of dispersion of insects or incidence of dead corn plants were related to distance.     

Design and synthesis of novel thiadiazole-thiazolone hybrids as potential inhibitors of the human mitotic kinesin Eg5

A novel series of 1,3,4-thiadiazole-thiazolone hybrids 5a–v were designed, synthesized, characterized, and evaluated against the basal and the microtubule (MT)-stimulated ATPase activity of Eg5. From the evaluated derivatives, 5h displayed the highest inhibition with an IC₅₀ value of 13.2?µM against the MT-stimulated Eg5 ATPase activity. Similarly, compounds 5f and 5i also presented encouraging inhibition with IC₅₀ of 17.2?µM and 20.2?µM, respectively. A brief structure–activity relationship (SAR) analysis indicated that 2-chloro and 4-nitro substituents on the phenyl ring of the thiazolone motif contributed significantly to enzyme inhibition. An in silico molecular docking study using the crystal structure of Eg5 further supported the SAR and reasoned the importance of crucial molecular protein–ligand interactions in influencing the inhibition of the ATPase activity of Eg5. The magnitude of the electron-withdrawing functionalities over the hybrids and the critical molecular interactions contributed towards higher in vitro potency of the compounds. The drug-like properties of the synthesized compounds 5a–v were also calculated based on the Lipinski’s rule of five and in silico computation of key pharmacokinetic parameters (ADME). Thus, the present work unveils these hybrid molecules as novel Eg5 inhibitors with promising drug-like properties for future development.     

Rational Assembly of Hollow Microporous Carbon Spheres as P Hosts for Long‐Life Sodium‐Ion Batteries

This paper reports the rational assembly of novel hollow porous carbon nanospheres (HPCNSs) as the hosts of phosphorous (P) active materials for high‐performance sodium‐ion batteries (SIBs). The vaporization‐condensation process is employed to synthesize P/C composites, which is elucidated by both theories and experiments to achieve optimized designs. The combined molecular dynamics simulations and density functional theory calculations indicate that the morphologies of polymeric P₄ and the P loading in the P/C composites depend mainly on the pore size and surface condition of carbon supports. Micropores of 1–2 nm in diameter and oxygenated functional groups attached on carbon surface are essential for achieving high P loading and excellent structural stability. In light of these findings, HPCNS/amorphous red phosphorus composites with enhanced structural/functional features are synthesized, which present an extremely low volume expansion of ≈67.3% during cycles, much smaller than the commercial red P's theoretical value of ≈300%. The composite anodes deliver an exceptional sodium storage capacity and remarkable long‐life cyclic stability with capacity retention over 76% after 1000 cycles. This work signifies the importance of rational design of electrode materials based on accurate theoretical predictions and sheds light on future development of cost‐effective P/C composite anodes for commercially viable SIBs.     

Template-directed synthesis and selective adsorption of oligoadenylates on hydroxyapatite

Summary Polyuridylic acid is adsorbed completely from aqueous solution by hydroxyapatite under conditions that permit template-directed synthesis of oligoadenylates in free solution. The yield of oligoadenylates is enhanced to almost the same extent by poly(U) in the presence or the absence of hydroxyapatite. Under very similar conditions small quantities of hydroxyapatite adsorb higher molecular-weight oligoadenylates selectively from a mixture of oligomers.On the basis of these results we propose a mechanism for prebiotic oligonucleotide formation in which selective adsorption on hydroxyapatite or some other immobilized anion-exchanging material plays a major role. Monomers are released from the surface for reactivation, while oligomers are retained in a protected environment by adsorption to the apatite surface.Abbreviations poly(U) polyuridylate - HA hydroxyapatite - ImpA adenosine 5-phosphorimidazolide - pA adenosine 5-phosphate - ADP adenosine 5-diphosphate - MeIm 1-methylimidazole - EDTA ethylenediaminetetraacetic acid - (pA)_n (n = 2, 3, 4) oligoadenylates with 5-terminal phosphates The nature of the internucleotide linkages is not specifiedThe nature of the internucleotide linkages is not specified