Evolutionary patterns of the mitochondrial genome in the Moorish gecko, Tarentola mauritanica

A previous study on the evolutionary patterns of Tarentola mauritanica demonstrated that low levels of mitochondrial diversity observed in the European populations relative to nuclear markers were consistent with a selective sweep hypothesis. In order to unravel the mitochondrial evolutionary history in this European population and two other lineages of T. mauritanica (Iberian and North African clades), variation within 22 nearly complete mitogenomes was analyzed. Surprisingly, each clade seems to have a distinct evolutionary history; with both the European and Iberian clades presenting a decrease of polymorphism, which in the former is consistent with departure from neutrality of the mtDNA (positive or background selection), but in the latter seems to be the result of a bottleneck after a population expansion. The pattern exhibited by the North African clade seems to be a consequence of adaptation to certain mtDNA variants by positive selection.     

Catalytic Turnover Triggers Exchange of Subunits of the Magnesium Chelatase AAA+ Motor Unit

The ATP-dependent insertion of Mg²⁺ into protoporphyrin IX is the first committed step in the chlorophyll biosynthetic pathway. The reaction is catalyzed by magnesium chelatase, which consists of three gene products: BchI, BchD, and BchH. The BchI and BchD subunits belong to the family of AAA+ proteins (ATPases associated with various cellular activities) and form a two-ring complex with six BchI subunits in one layer and six BchD subunits in the other layer. This BchID complex is a two-layered trimer of dimers with the ATP binding site located at the interface between two neighboring BchI subunits. ATP hydrolysis by the BchID motor unit fuels the insertion of Mg²⁺ into the porphyrin by the BchH subunit. In the present study, we explored mutations that were originally identified in semidominant barley (Hordeum vulgare L.) mutants. The resulting recombinant BchI proteins have marginal ATPase activity and cannot contribute to magnesium chelatase activity although they apparently form structurally correct complexes with BchD. Mixing experiments with modified and wild-type BchI in various combinations showed that an exchange of BchI subunits in magnesium chelatase occurs during the catalytic cycle, which indicates that dissociation of the complex may be part of the reaction mechanism related to product release. Mixing experiments also showed that more than three functional interfaces in the BchI ring structure are required for magnesium chelatase activity.     

平肝熄风汤联合硫酸镁对肝肾阴虚型妊娠期高血压患者血液动力学、糖脂代谢及妊娠结局的影响

摘要 目的：探讨平肝熄风汤联合硫酸镁对肝肾阴虚型妊娠期高血压（GH）患者血液动力学、糖脂代谢及妊娠结局的影响。方法：选取2018年3月~2019年10月期间兰州市第二人民医院收治的GH 患者119例随机分为对照组（n=59）和研究组（n=60）,对照组给予硫酸镁治疗,研究组在对照组的基础上联合平肝熄风汤治疗,比较两组患者疗效、血液动力学、糖脂代谢、血压、心率、中医证候积分及妊娠结局。结果：研究组治疗7 d后的临床总有效率为91.67%（55/60）,明显高于对照组的77.97%（46/59）（P<0.05）。两组治疗7 d后收缩压、舒张压、平均动脉压、心率均下降,且研究组低于对照组（P<0.05）。两组治疗7 d后心输出量（CO）、心脏指数（CI）均下降,且研究组低于对照组（P<0.05）。两组治疗7 d后甘油三酯（TG）、低密度脂蛋白 （LDL-C）、空腹血糖、总胆固醇（TC）水平降低,高密度脂蛋白 （HDL-C）水平升高（P<0.05）,且研究组变化程度大于对照组（P<0.05）。两组治疗7 d后视物模糊、手足心热、脉弦细数、口干便结、舌红苔少等症状评分均下降,且研究组低于对照组（P<0.05）。研究组不良妊娠结局发生率低于对照组（P＜0.05）。结论：平肝熄风汤联合硫酸镁治疗肝肾阴虚型GH,疗效显著,可有效改善患者临床症状、血液动力学、糖脂代谢,同时还可减少不良妊娠结局发生率,临床应用价值较高。     

Evidence for ditopic coordination of phosphate diesters to [Mg(15-crown-5)]<Superscript>2+</Superscript>. Implications for magnesium biocoordination chemistry

The interaction of a series of phosphate diesters and triesters (1=diphenyl phosphate, 2=dimethyl phosphate, 3=bis(2-ethylhexyl) phosphate, 4=trimethyl phosphate, 5=methyldiphenyl phosphate, 6=triphenyl phosphate) with [Mg(15-crown-5)]²⁺ (15-crown-5=1,4,7,10,13-pentaoxocyclopentadecane) was studied as a simplified model for the interaction of aqueous Mg²⁺ ion with phosphate-containing biomolecules such as RNA. Using electrospray mass spectrometry, we confirm the formation of 1:1 adducts in the gas phase. Proton and ³¹P NMR titration data were used to construct binding isotherms, and a 1:1 binding equilibrium was fit to the isotherms at room temperature to estimate the binding affinities. The binding affinity data are consistent with ditopic coordination of neutral dialkyl phosphate ligands to the [Mg(15-crown-5)]²⁺ unit. This involves inner-sphere coordination to the Mg²⁺ via an oxygen atom, which is complemented by a weak hydrogen-bonding interaction with the crown ether ligand. Ditopic interaction is consistent with low-temperature NMR spectra showing four different configurations for 1 coordinated to [Mg(15-crown-5)]²⁺, which are interpreted in terms of hindered rotation around the Mg–O_phos bond. Thermochemical analysis of the binding affinity data suggests that the second-shell interaction contributes only about 1 kcal/mol to the binding free energy, so additional factors, such as steric constraints, must be operative to give a preferred phosphate orientation in this system. However, the experimental data do suggest that second-shell interactions contribute as much as 40% of the total binding energy, consistent with the pronounced ability of aqueous Mg²⁺ to form salt-bridges linking secondary and tertiary elements of RNA structure.Abbreviations OTf trifluoromethanesulfonate - ESI-MS electrospray mass spectrometry     

Double-strand hydrolysis of DNA by a magnesium(II) complex with diethylenetriamine

The development of artificial nucleases that hydrolyze DNA or RNA is of great interest in molecular biology, biotechnology, and medicine. We now report that a magnesium(II) complex of diethylenetriamine (Mg-dien) can effectively promote the double-stranded cleavage of plasmid DNA and the dideoxynucleotide dApdA under physiological conditions of pH and temperature. Experiments performed in the presence of hydrogen peroxide, radical scavengers, or under rigorously anaerobic conditions indicate that DNA cleavage mediated by Mg-dien occurs via a hydrolytic path. Mg-dien efficiently hydrolyzes supercoiled pBR322 DNA and the pseudo-first-order rate constant at 37 degrees C and pH 8.0 is estimated to be 1.60 h(-1). The dinucleotide dApdA hydrolysis, with Mg-dien at 170 microM, shows a rate enhancement factor of ca. 5 x 10(8). 1H and 31P(1H) NMR studies show that Mg-dien effectively hydrolyzes 5'-dAMP to give deoxyadenosine and inorganic phosphate. While Mg2+ has been found at the catalytic sites of many natural nucleases, Mg-dien appears to be the first synthetic Mg2+-containing system capable of hydrolyzing dideoxynucleotides and DNA and thus may provide a simple model system to assist mechanistic studies of naturally occurring nucleases.     

Abnormal magnesium metabolism in etiology of salt-sensitive hypertension and type 2 diabetes mellitus

A previously unknown genetic defect in magnesium metabolism (i.e., the magnesium-binding defect [MgBD]) was found to be associated with the cause of “salt-sensitive” essential hypertension in humans and rats. It inhibits the entrance of Mg²⁺ into the cell so that the intracellular concentrations of Mg²⁺ and MgATP²⁻ are decreased. Consequently, the 300 enzyme reactions in the cell, especially the 100 that either use or produce MgATP²⁻, are inhibited. Thus, because the extrusion of intracellular Na⁺ requires MgATP²⁻, hypertension results when the involved MgATP²⁻ requiring enzyme is inhibited. The MgBD is corrected by the tachykinin substance P, which occurs in normal blood plasma, and by the pentapeptide and its contained tetrapeptide, which are released from the C-terminal region of substance P by plasma aminopeptidases. In vivo, the intravenous administration of the tetrapeptide corrects the hypertension and the MgBD as well. The MgBD also occurs in type 2 diabetes mellitus and, thus, the decreased intracellular concentrations of Mg²⁺ and MgATP²⁻ ions appear to be involved also in the cause of this disease, which is reputed to be the fifth most deadly disease in the world.     

Effects of magnesium sulfate on energy metabolites and glutamate in the cortex during focal cerebral ischemia and reperfusion in the gerbil monitored by a dual-probe microdialysis technique

Previous studies have demonstrated that magnesium sulfate has cytoprotective properties for treating experimental rat brain injuries. The aim of this study is to evaluate changes in energy-related metabolites and glutamate in the cortex of gerbils subjected to focal cerebral ischemia with the pretreatment of magnesium sulfate. The focal cerebral ischemia was produced by the occlusion of the right common carotid artery and the right middle cerebral artery for 60 mins. A significant decrease in infarct size was found in the magnesium sulfate treated group when compared to the controls. Two microdialysis probes were inserted bilaterally into the cortex to monitor extracellular glucose, lactate, pyruvate and glutamate during cerebral ischemia and reperfusion periods. The present study showed a dynamic decrease of glucose (10% of the baseline), pyruvate (15% of the baseline), and an increase of lactate (200% of the baseline) and glutamate (1400% of the baseline) on the ipsilateral side during ischemia in the control group. Magnesium sulfate significantly preserved glucose (up to 50% of the baseline) and pyruvate (70% of the baseline) levels in the ipsilateral side during ischemia. There was significant attenuation in the elevation of glutamate and lactate (500% and 150% of the baseline, respectively) when treatments of magnesium sulfate were administered. No significant influence on these neurochemicals in the contralateral side was observed in either group. These results suggest that both the preservation of cellular energy metabolism, and the attenuation of glutamate release during cerebral ischemia and after restoration of reperfusion may contribute to the neuroprotective effects of magnesium sulfate.     

Glucose-induced alterations of intracellular ionized magnesium in human lymphocytes

The intracellular ionic content of human erythrocytes may be altered by hyperglycaemia. Despite this, very little is known about the cellular mechanisms linking glucose and cellular magnesium homeostasis. We measured intracellular ionized magnesium in human lymphocytes, by means of a fluorimetric technique, total intracellular magnesium by means of atomic absorption spectrophotometry and intracellular ATP by means of HPLC. The incubation of lymphocytes with D-glucose in the absence of insulin was followed by a significant decrease in intracellular ionized magnesium; this effect did not occur when the cells were incubated with L-glucose. The effect of glucose on intracellular ionized magnesium was blocked by amphotericin B and the EC(50) of the effect of glucose on intracellular ionized magnesium was about 5 mmol/l of glucose. The increase of intracellular ionized magnesium in cells incubated in the absence of glucose was followed by a decrease in intracellular ATP. In a Na(+)-free medium the decrease of intracellular ionized magnesium in the presence of glucose was still present and the incubation of lymphocytes with glucose did not modify total intralymphocyte magnesium. By selective permeabilization of cell membranes, we established that glucose could not increase compartmentalized intracellular ionized magnesium. Our data supports the hypothesis that glucose per se induces a substantial decrease in intracellular ionized magnesium, which is probably due to an augmented binding of intracellular ionized magnesium to cellular ATP.     

The impact of the paper of Edsall and Mehl (1940) on actin and actomyosin research

The paper of Edsall and Mehl, ‘The effect of denaturing agents on myosin, II. Viscosity and double refraction of flow’, J. Biol. Chem. 133 (1940) 409–429, inspired our research on actin and actomyosin. It led to the specific purification of actin with magnesium ions and to the demonstration of the central role of the Mg²⁺-activated actomyosin ATPase in contraction of live muscle.     

Osteogenesis promoted by calcium phosphate N,N-dicarboxymethyl chitosan

The effects of N,N-dicarboxymethyl chitosan (DCMC) on the precipitation of insoluble calcium salts, namely phosphate, sulfate, oxalate, carbonate, bicarbonate and fluoride, and magnesium salts, namely phosphate and carbonate, were studied. Results indicated that the chelating ability of DCMC interfered effectively with the well-known physico-chemical behaviour of magnesium and calcium salts. Dicarboxymethyl chitosan formed self-sustaining gels upon mixing with calcium acetate, as a consequence of calcium chelation. DCMC mixed with calcium acetate and with disodium hydrogen phosphate in appropriate ratios (molar ratio Ca/DCMC close to 2.4) yielded a clear solution, from which, after dialysis and freeze-drying, an amorphous material was isolated containing an inorganic component about one half its weight. This compound was used for the treatment of bone lesions in experimental surgery and in dentistry. Bone tissue regeneration was promoted in sheep, leading to complete healing of otherwise non-healing surgical defects. Radiographic evidence of bone regeneration was observed in human patients undergoing apicectomies and avulsions. The DCMC–CaP chelate favoured osteogenesis while promoting bone mineralization.