Quantum-chemical investigation of the elementary molecular mechanisms of pyrimidine-purine transversions

Purine-purine mispairs of DNA (thus involving template base in anti-conformation along the glycosidic bond and base of the incoming nucleotide - in syn-conformation) leading to pyrimidine-purine "transversions"-type point mutations were revealed and characterized at the MP2/6-311++G(2df,pd)//B3LYP/6-311++G(d,p) level of theory in vacuum approach adequately modeling hydrophobic environment of the active centre of high-fidelity replicative DNA-polymerases.     

Synthesis of polyglycerol phosphate by Bacillus stearothermophilus.

A particulate enzyme preparation from Bacillus stearothermophilus synthesized 1,3-poly(glycerol phosphage) from CDPglycerol at an optimum pH of 8.0 and the reaction was stimulated by divalent cations. Km for CDPglycerol was 0.18 mM. The synthesis was inhibited by CMP, CDP, and CTP and by concentrations of CDP-glycerol above 0.49 mM. The reaction was irreversible, The product had an average chain length of 8 glycerol units. About two thirds of the polymers were synthesized in entirety while the ramainder were attached to some acceptor by their phosphate end. The enzome was able to synthesize only a limited amount of polymer.     

Can DNA-binding proteins of replisome tautomerize nucleotide bases? Ab initio model study

Ab initio quantum-chemical study of specific point contacts of replisome proteins with DNA modeled by acetic acid with canonical and mutagenic tautomers of DNA bases methylated at the glycosidic nitrogen atoms was performed in vacuo and continuum with a low dielectric constant (??～?4) corresponding to a hydrophobic interface of protein-nucleic acid interaction. All tautomerized complexes were found to be dynamically unstable, because the electronic energies of their back-reaction barriers do not exceed zero-point vibrational energies associated with the vibrational modes whose harmonic vibrational frequencies become imaginary in the transition states of the tautomerization reaction. Additionally, based on the physicochemical arguments, it was demonstrated that the effects of biomolecular environment cannot ensure dynamic stabilization. This result allows suggesting that hypothetically generated by DNA-binding proteins of replisome rare tautomers will have no impact on the total spontaneous mutation due to the low reverse barrier allowing a quick return to the canonical form.     

Dynamic compression counteracts IL-1β induced inducible nitric oxide synthase and cyclo-oxygenase-2 expression in chondrocyte/agarose constructs

Background  

Nitric oxide and prostaglandin E₂ (PGE₂play pivotal roles in both the pathogenesis of osteoarthritis and catabolic processes in articular cartilage. These mediators are influenced by both IL-1β and mechanical loading, and involve alterations in the inducible nitric oxide synthase (iNOS) and cyclo-oxygenase (COX)-2 enzymes. To identify the specific interactions that are activated by both types of stimuli, we examined the effects of dynamic compression on levels of expression of iNOS and COX-2 and involvement of the p38 mitogen-activated protein kinase (MAPK) pathway.     

Molecular mechanisms of transitions induced by cytosine analogue: comparative quantum-chemical study

Using the simplest molecular models at the MP2/6-311++G(2df,pd)//B3LYP/6-311++G(d,p) level of the theory it has been shown for the first time that in addition to traditional incorporational errors caused by facilitated (compared with the canonical DNA bases cytosine (Cyt)) tautomerization of 6-(2-deoxy-beta-D-ribofuranosyl)-3,4-dihydro-6H,8H-pyrimido[4,5-c][1,2]oxazin-7-one (DCyt), this mutagen causes the replication errors, increasing one million times the population of mispair Gua.DCyt* (asterisk marked mutagenic tautomer) as compared with mispair Gua.Cyt*. It is also proved that DCyt in addition to traditional incorporational errors also induces similar errors by an additional mechanism - due to a facilitated tautomerization of the wobble base pair Ade.DCyt (compared to the same pair Ade.Cyt) to a mispair Ade.DCyt* which is quasirisomorphic Watson-Crick base pair. Moreover, the obtained results allowed interpreting non-inconsistently the existing experimental NMR data.     

Quantum-chemical investigation of tautomerization ways of Watson-Crick DNA base pair guanine-cytosine

A novel physico-chemical mechanism of the Watson-Crick DNA base pair Gua.Cyt tautomerization Gua.Cyt*<---->Gua.Cyt<---->Gua*.Cyt (mutagenic tautomers of bases are marked by asterisks) have been revealed and realized in a pathway of single proton transfer through two mutual isoenergetic transition states with Gibbs free energy of activation 30.4 and 30.6 kcal/mol and they are ion pairs stabilized by three (N2H...N3, N1H...N4- and O6+H...N4-) and five (N2H...O2, N1H...O2, N1H...N3, O6+H...N4- and 06+H...N4-) H-bonds accordingly. Stable base pairs Gua-Cyt* and Gua*.Cyt which dissociate comparably easy into monomers have acceptable relative Gibbs energies--12.9 and 14.3 kcal/mol--for the explanation of the nature of the spontaneous transitions of DNA replication. Results are obtained at the MP2/6-311++G(2df,pd)//B3LYP/6-31 1++G(d,p) level of theory in vacuum approach.     

文山松毛虫质型多角体病毒形态结构及理化性质的研究

对文山松毛虫质型多角体病毒的形态结构及理化特性进行了研究,多角体大部分为六边形,少数为四边形及近园形,其大小在0.47～2.45μ之间,平均为1.1μ。病毒粒子呈球形,无囊膜,致密的核芯区由一层外壳包裹,直径为60nm。病毒粒子表面有12个刺突,放大图象可见其亚单位排列。多角体蛋白的主要成分为一种,分子量为26200道尔顿,多角体蛋白氨基酸组成中不含半胱氨酸;其碱性氨基酸与酸性氨基酸之比为1:2.16。病毒粒子结构蛋白含五条多肽组分。用SDS-热酚法提取所得核酸,其热变性紫外吸收OD_(260)值增加51.6％。抗核酸酶S_1。Tm值为86℃。在1％琼脂糖凝胶电泳中可分为9个片段,而在5％PAGE中,则可分为10个片段。各片段大小在0.66×10~6～2.85×10~6道尔顿之间,总分子量为15.35×10~6。电镜分析研究显示了CPV RNA在0.4μ、0.8μ和1.2μ处有三个分布峰。     

An Investigation into the Rate and Control of Assimilate Movement from Leaves in Pisum sativum

Export studies were made on leaves of Pisum by monitoring the¹⁴CO₂-treated source leaf at its surface at frequent intervals.Radiocarbon levels of fresh leaf samples showed a good correlationwith results from the more conventional methods of radiocarbonestimation which involve destructive analysis. The rate of export was highest in plants which had been defoliated,except for the source leaf 20 h or more before the start ofthe export study. Removal of the shoot apex reduced export andprogressive reduction in sink capacity was associated with decreasedexport rates, particularly over short time periods. Export rateswere similar in defoliated and non-defoliated plants where theshoot apex and the roots had been excised. This suggested thata decrease in the source resulted in higher export rates fromthe remaining source only when active sinks were present; thisin turn suggests that, at least under these conditions, activeremoval of photosynthate is more important in controlling exportthan the photosynthate build-up in the leaf itself. The non-destructive technique enabled comparisons to be madebetween export curves for individual plants. It was found thatin experiments replicated in time, the same relationship betweentreatments was present on different days and the shape of theexport curves was similar but the absolute values for exportedradiocarbon sometimes varied considerably.     

Chilling-induced Lipid Hydrolysis in the Oil Palm (Elaeis guineensis) Mesocarp

Oil palm fruits exposed to temperatures of 15 °C and belowshowed a significant increase in free fatty acid (FFA) contentin the mesocarp. This effect was most pronounced in fruits exposedto 5 °C when FFA levels exceeding 70% of the total oil wereobserved. The increase in FFA was accompanied by an increasein lipid-soluble phosphorus levels and a decrease in carotenecontent. Chilling did not have an effect on palm kernel oil.The results suggest the activation of a lipase in the mesocarpby low temperature stress. Key words: Lipase, oil palm, free fatty acid