Room temperature solvent extraction for simple and fast determination of total concentration of Ca,Cu, Fe,Mg, Mn,and Zn in bee pollen by FAAS along with assessment of the bioaccessible fraction of these elements using in vitro gastrointestinal digestion

Background and aimBee pollen is recognized to be a source of different nutrients, including minerals. As a food supplement, its quality and safety due to concentrations of essential macro- and microelements, and harmful trace elements has to be verified. Fast and simple element analysis of bee-collected pollen can be regarded as an important part of its quality assurance and control. The present study aimed at developping a new method for determination of selected elements (Ca, Cu, Fe, Mg, Mn, Zn) of bee pollen based on solvent extraction and completely avoiding a high temperature treatment with concentrated reagents. In addition, in vitro gastrointestinal digestion was used to assess bioavailability of elements from this food supplement.MethodsBee pollen samples were dried and pulverized. Total concentrations of Ca, Cu, Fe, Mg, Mn, and Zn were determined by flame atomic absorption spectrometry (FAAS) in sample solutions obtained by wet digestion (WD) in concentrated HNO₃ or alternatively by solvent extraction (SE) with diluted solutions of HNO₃. Gastrointestinal digestion was mimicked using simulated solutions of gastric and intestinal juices followed by determination of Ca, Cu, Fe, Mg, Mn and Zn concentrations in the bioaccessible fraction by FAAS.ResultsA new simple and fast method for determination of total concentrations of Ca, Cu, Fe, Mg, Mn, and Zn in bee pollen was developed and validated. The method combined room temperature, two-hour SE with 0.5 mol L⁻¹ HNO₃ with FAAS measurements versus simple standard solutions. It provided precision within 1–5 % and trueness better than 8%, and was shown to be suitable for fast analysis of different polyfloral bee pollens. In vitro gastrointestinal digestion revealed that elements were well (70–85 % for Ca, Mg) and fairly (27–43 % for Cu, Fe, Mn, and Zn) bioaccessible from bee pollen. By pouring with water and swelling overnight, bioaccessibility of studied elements from such prepared bee pollen was increased on average by less than 15 % (Mn), 20 % (Ca, Cu, Fe, Zn) or 30 % (Mn).ConclusionsAvoiding long-lasting, high-temperature wet digestion with concentrated reagents, the proposed sample treatment along with FAAS provided precise and true results of total concentrations of Ca, Cu, Fe, Mg, Mn, and Zn in bee pollen. The method was simple and fast, and enabled to analyze a higher number of samples. Simulated gastrointestinal digestion of bee pollen have shown for the first time that Ca and Mg are the most bioaccessible from this bee product. Bioaccessibility of Cu, Fe, Mg, and Zn from bee pollen are close to or lower than 40 %.     

Active uptake of aluminium,copper and manganese by the freshwater amphipod Paramelita nigroculus in acidic waters

Experiments were performed on the freshwater amphipod Paramelita nigroculus to determine the route of uptake for Al, Cu and Mn. The extent of correlation between the concentrations of Al, Cu and Mn and those of macro-cations Na, Ca and Mg was investigated in order to determine appropriate strategies of water quality management. Indeed, active uptake of toxicants can be controlled by disturbing the active pump used. After 21 days of exposure to different combined concentrations, survivors were analysed chemically by ICP-S after depuration, drying, ashing and digestion with concentrated nitric acid.The results showed significant correlations between the concentrations of major cations and the three metals under study (i.e. Al, Cu and Mn) at p < 0.05. These are Ca vs Al, Ca vs Mg, Na vs Mg, Na vs Mn, Al vs Mg, Al vs Cu, and Mg vs Mn. No other combination showed significant correlation. High r-values for Na vs Mg (r=0.7194) and for Na vs Mn (r=0.6253), as well as low concentrations of Mg and Mn, suggest interactions between the active uptake of Mn and Mg, although there may be interferences due to the use of Na pump. Additional experiments examined the type of interaction occurring when Mn and Mg were present in 1:1 mixtures in water. The Student's t test showed that observed differences in bioaccumulation of Mn, when alone and when combined, were not statistically significant at p < 0.05. These differences may be attributed to chance but not to the presence of Mg in the medium; while differences in bioaccumulation of Mg, when alone and when combined, were statistically significant at p < 0.002. These were attributed to Mn, which lowers Mg uptake by P. nigroculus.     

On protein fractions and inorganic ions in sea urchin eggs,unfertilized and fertilized

Frozen and dried unfertilized or fertilized eggs were subjected to extraction by 1-N KCl solution according to the method inaugurated by Mirsky.In confirmation of Mirsky's results a certain protein fraction seemed to become insoluble in normal fertilization of the egg.The differences proved almost to vanish if the eggs prior to fertilization were subjected to trypsin treatment which removes the vitelline membrane and thus inhibits the formation of a continuous fertilization membrane.An obvious correlation was found between the percentage of extracted proteins and the salt content of the egg samples (fig. 1). This is particularly high in frozen and dried fertilized eggs with the fertilization membrane normally formed. This probably accounts entirely for the previously reported differences between unfertilized and fertilized eggs.Extraction of the frozen and thawed eggs with distilled water gave the same general picture as extraction with N KCl. Here also the solubility of the proteins is correlated with the salt content of the samples.The dialyzed water extracts gave a strong precipitation upon addition of Ca (optimum at 0.0125-0.025 M). Freezing and thawing of the extracts likewise cause a precipitation of a certain fraction.The fraction which becomes insoluble in the presence of high salt content of the sample and that precipitated from extracts by additions of Ca or by freezing and thawing seem to be identical. It contains the soluble nucleoprotein of the eggs.No changes in Ca or Mg content was found to occur upon fertilization of the egg.     

Two Ca2+ functions are demonstrated by the substitution of specific divalent and lanthanide cations for the Ca2+ required by the aggregation factor complex from the marine sponge, Microciona prolifera

Multivalent cations were tested for their ability to replace the Ca2+ requirements of aggregation factor (AF) complex in activity, stability, and integrity assays. The ability of each cation to replace the Ca2+ required for the cell aggregation-enhancing activity of AF was examined by replacing the usual 10 mM Ca2+ with the test cation at various concentrations in the serial dilution assay of the AF. The other alkaline earth cations, Mg2+, Sr2+, and Ba2+, could not replace Ca2+; two transition elements, Mn2+ and Cd2+, partially replaced calcium. All 15 of the available lanthanides (including La3+ and Y3+) produced normal activity but only at 10-400-fold lower cation concentrations than Ca2+. An AF preparation is stable and remains active for months in 1 mM Ca2+ but decays rapidly when Ca2+ is lowered. Sr2+ and Ba2+ at 20 mM but not at 1 mM could replace 1 mM Ca2+ and give long term stability. AF was not stable in the presence of Mg2+, even at 100 mM. High Mn2+ concentrations did not stabilize AF even though AF was partially active in Mn2+. Cd2+ gave full stability at 75 mM and La3+ at about 0.1 mM. When Ca2+ is chelated, the macromolecular subunits of the AF slowly dissociate. Permeation chromatography and analytical ultracentrifugation showed that the cations that stabilized activity maintained the integrity of AF complex while those that failed to stabilize activity allowed the complex to dissociate into subunits, indicating that these two Ca2+ requirements are related. The cation specificities for activity and for stability-integrity are different indicating that these are separate Ca2+-dependent functions.     

Effect of magnesium deficiency on enterocyte Ca, Fe, Cu, Zn, Mn and Se content

In previous studies based on indirect procedures, we reported that Mg deficit increased the bioavailability of a number of elements such as calcium, zinc, iron, copper, manganese and decreased selenium absorption. The present study was designed to verify these findings by direct methods. We investigated the effect of dietary magnesium deficiency on enterocyte Ca, Fe, Zn, Cu, Mn and Se concentrations. Male Wistar rats were fed a Mg-deficient diet (129 mg Mg/kg food) for 70 days. Whole enterocytes from the upper jejunum were isolated and Ca, Fe, Zn, Cu, Mn and Se were determined. The results were compared with findings in a control group that was pair-fed with an identical diet except that it covered this species's nutritional requirements for Mg (480 mg Mg/kg food). The Mg-deficient diet significantly increased enterocyte content of Ca, Fe, Zn, Cu and Mn; however, we found no significant changes in the Se content of these cells. These data support the results obtained by indirect methods.     

不同竹龄雷竹中硅及其他营养元素吸收和积累特征

在浙江省临安市的雷竹主产区,分别采集不同竹龄(1～4 a)和不同器官(叶、枝、秆)的雷竹样品,分析了Si和其他营养元素含量、吸收和积累特征,以及Si和其他营养元素之间的相互关系.结果表明： 雷竹各器官中C含量的大小顺序为竹秆>竹枝>竹叶,Si、N、P、K、Ca、Mg、Al、Fe和Mn含量的大小顺序为竹叶>竹枝>竹秆.除Mn主要积累在竹叶中外,其他9种营养元素主要积累在1年生雷竹的秆中.3～4年生雷竹竹叶的Si平均含量为13.66 g · kg^-1. 雷竹属于Si积累植物.随竹龄的增加,雷竹叶中的N、P、K和Mg含量减少,C、Al和Mn含量增加.雷竹对Si的吸收主要集中在第2年(57.1%),对N和K的吸收主要集中在前两年(67.7%～93.7%),此后N和K从植株体内流出,其流失量分别占总积累量的19.1%～39.1%.雷竹中Si与Ca、Al、Mn呈显著正相关,与N、P、K、Mg呈显著负相关.     

Effect of different iron-, potassium-, phosphate-, and calcium-manganese relationships on the growth and chemical composition of aromatic strain of bidi tobacco (Nicotiana tabacum L.)

Summary In order to study the Mn nutrition ofbidi tobacco plant (Nicotiana tabacum L. aromatic strain 2-1) when it is supplied with nutrient solutions containing different ratios of Mn with Fe, P, K and Ca, a sand-culture experiment was carried out in four different series viz. Fe-Mn, K-Mn, P-Mn and Ca-Mn. No characteristic deficiency symptoms except general loss of green colour and diminished growth were observed at 0.1 ppm Mn in the nutrient solution. Toxicity was observed when Mn in the nutrient solution was 100 ppm and severity of the symptoms decreased with increase in Fe-Mn or K-Mn ratios, but it increased when P-Mn ratio increased while in Ca-Mn series it first decreased and then increased at still higher concentration of Ca on account of chloride ion effect as CaCl₂ had to be added to bring about 500 ppm concentration of Ca necessary for the treatment. No symptoms of deficiency or toxicity were observed when Mn in nutrient solution varied from 1 to 10 ppm and Fe-Mn ratio for the leaf varied from 0.4 to 6.1 and its Mn content varied from 190 to 1575 ppm. Slight loss of green colour and plant vigour appeared when Fe-Mn ratio for the leaf was higher than 12.8 even though the Mn content was as high as 90 ppm. Toxic effect due to excessive Mn was felt when Fe-Mn ratio was 0.35 or less and leaf content 1875 ppm or more. Nicotine content was inversely related to the intensity of Mn-toxicity.Contribution from the Agricultural Chemistry and Soil Science Division, Institute of Agriculture, Anand, G.S., India.Prof. and Head of the Agricultural Chemistry and Soil Science Division, and Lecturer in Agricultural Chemistry, respectively.     

Distribution of N,P, K,Ca, Mg,S, Zn,Fe, Mn and Cu in groundnut

Summary Concentration of N, P, K, Ca, Mg and S in summer groundnut crop was higher than in kharif while Zn, Fe, Mn and Cu contents were higher in summer crop. Kernel's N, P and Zn; Leaflet's Ca and Mn; Stem's K and Fe; Root's S and Cu and Petiole's Mg contents were highest. Shell's N, P, K, Mg, S, Zn and Cu; Kernel's Ca, Fe and Mn contents were the least. N, P, K, S, Zn and Cu concentrations decreased linearly as the crop grew. Ca, Mg, Fe and Mn concentrations did not display any distinct pattern. Ca concentration was positively correlated with pod yield in both the seasons.     

Minor and trace elements in human milk from Guatemala,Hungary, Nigeria,Philippines, Sweden,and Zaire

Concentrations of As, Ca, Cd, Cl, Co, Cr, Cu, F, Fe, Hg, I, K, Mg, Mn, Mo, Na, Ni, P, Pb, Sb, Se, Sn, V, and Zn were determined in human whole milk samples from Guatemala, Hungary, Nigeria, Philippines, Sweden, and Zaire; in most of these countries, three groups of subjects representing different socioeconomic conditions were studied. Analytical quality control was a primary consideration throughout. The analytical techniques used were atomic absorption spectrophotometry, atomic emission spectrometry with an inductively coupled plasma, colorimetry, electrochemistry, using an ion-selective electrode and neutron activation analysis. The differences between median concentrations of Ca, Cl, Mg, K, Na, and P (minor elements) were lower than 20% among the six countries. Among trace elements, concentrations observed in Filipino milk for As, Cd, Co, Cr, Cu, F, Fe, Mn, Mo, Ni, Pb, Sb, Se, and V were higher than for milk samples from other countries. The remaining five countries showed a mixed picture of high and low values. In the case of at least some elements, such as, F, I, Hg, Mn, Pb, and Se, the environment appears to play a major role in determining their concentrations in human milk. The nutritional status of the mother, as reflected by her socioeconomic status, does not appear to influence significantly the breast milk concentrations of minor and trace elements. Significant differences exist between the actual daily intakes observed in this study and current dietary recommendations made by, for example, WHO and the US National Academy of Sciences. These differences are particularly large (an order of magnitude or more!) for Cr, F, Fe, Mn, and Mo; for other elements, such as, Ca, Cu, Mg, P, and Zn, they amount to at least a factor 2. In the opinion of the present authors, these findings point to the need for a possible reassessment of the dietary requirements of young infants with respect to minor and trace elements, particularly for the elements Ca, Cr, Cu, F, Fe, Mg, Mn, Mo, P, and Zn.     

Stability studies of amphetamine and ephedrine derivatives in urine

Knowledge of the stability of drugs in biological specimens is a critical consideration for the interpretation of analytical results. Identification of proper storage conditions has been a matter of concern for most toxicology laboratories (both clinical and forensic), and the stability of drugs of abuse has been extensively studied. This concern should be extended to other areas of analytical chemistry like antidoping control. In this work, the stability of ephedrine derivatives (ephedrine, norephedrine, methylephedrine, pseudoephedrine, and norpseudoephedrine), and amphetamine derivatives (amphetamine, methamphetamine, 3,4-methylenedioxyamphetamine (MDA), and 3,4-methylenedioxymethamphetamine (MDMA)) in urine has been studied. Spiked urine samples were prepared for stability testing. Urine samples were quantified by GC/NPD or GC/MS. The homogeneity of each batch of sample was verified before starting the stability study. The stability of analytes was evaluated in sterilized and non-sterilized urine samples at different storage conditions. For long-term stability testing, analyte concentration in urine stored at 4 degrees C and -20 degrees C was determined at different time intervals for 24 months for sterile urine samples, and for 6 months for non-sterile samples. For short-term stability testing, analyte concentration was evaluated in liquid urine stored at 37 degrees C for 7 days. The effect of repeated freezing (at -20 degrees C) and thawing (at room temperature) was also studied in sterile urine for up to three cycles. No significant loss of the analytes under study was observed at any of the investigated conditions. These results show the feasibility of preparing reference materials containing ephedrine and amphetamine derivatives to be used for quality control purposes.     

Effects of sodium, potassium and calcium on salt-stressed barley

We grew barley ( Hordeum vulgare L. CM 72) for a 28-day period and sequentially harvested plants every 3 or 4 days. Plants were salt-stressed with either NaCl or KCl (125 m M ) with or without supplemental Ca (10 or 0.4 m M final concentration, respectively). We determined tissue concentrations of Na, Ca, Mg, K. S, P, Fe, Mn, Cu and Zn for each harvest date by inductively coupled plasma spectrometry. Uptake (specific absorption rate) was calculated from the element content and growth rates. Salinity had significant effects on the uptake and concentrations of most elements. Mg and Mn concentrations declined with time. The concentrations of all other elements determined increased over time. Element uptake on a root dry weight basis declined with time. Three variables were significantly affected by salinity and correlated with growth; 1) the Ca concentration, 2) the total sum of the cation concentration (TC), and 3) the Mn concentration of the shoot. Salinity reduced Ca uptake and concentrations. Supplemental Ca increased Ca concentrations and was positively correlated with growth during salt stress. Salinity doubled TC, which was negatively correlated with relative growth rate (RGR). Relative growth rate declined at TC values above 150 m M . Salinity reduced the uptake and concentration of Mn. Manganese concentrations in the shoot were highly correlated with RGR. Relative growth rate declined at Mn concentrations below 50 nmol (g fresh weight)⁻¹.     

Inactivation and reactivation of rat liver 3-hydroxy-3-methylglutaryl-CoA-reductase phosphatases: effect of phosphate, pyrophosphate and divalent cations

Incubation of four purified rat liver HMG-CoA-reductase phosphatases (Gil, G., Sitges, M. and Hegardt, F.G. (1981) Biochim. Biophys. Acta 663, 211-221) with Mn2 or Mg2 caused a concentration-dependent activation of enzyme activities. The maximum effect for Mn2 was at 5 mM for all phosphatases. Fe2 caused inactivation only in reductase phosphatases IIa and IIb. Ca2 10 mM showed a slight effect of inactivation. Phosphate, pyrophosphate and adenine nucleotides inhibited the four reductase phosphatases, this process being concentration-dependent. cAMP did not inhibit the four phosphatases at all in the range of 0.01-8 mM. Preincubation of reductase phosphatases with PPi and subsequent dilution did not diminish the inactivation effect, showing that this ion inhibits the enzyme prior to the binding to the substrate. Phosphorylated sugars, but not free sugar, inactivated the four reductase phosphatases. PPi-inactivated enzymes were reactivated by Mg2 or Mn2, this process being time-dependent. The four phosphatases had different patterns of reactivation. Phosphatases Ib and IIb (low-molecular mass forms) were shown to be different enzymes as judged by: their divergent behaviour when inhibited with Fe2; their PPi response; kinetics of reactivation by Mg2 or Mn2 or PPi-inactivated enzymes; and thermal stability. A metalloenzyme character is suggested for reductase phosphatases.     

Evaluation of sewage sludge, septic waste and sludge compost applications to corn and forage: Ca, Mg, S, Fe, Mn, Cu, Zn and B content of crops and soils

This is the second of two papers presenting the data from an experiment on the application of aerobically-digested sewage sludge (AES), anaerobic lagoon septic wastes (ANS), sewage sludge compost and fertilizer to soils for grass forage and feed corn production at two different sites in Nova Scotia. Crop yields, plant tissue and Mehlich-1 extractable soil nutrients were evaluated; 15 elements were analyzed in the plant tissue and 9 elements in the soil extracts. This paper describes the Ca, Mg, S, Fe, Mn, Cu, Zn and B content of the crops and the Mehlich-1 extractable content of the soils. The response to the amendments was not consistent at the two sites with the two different crops. We found that the septic sludge (ANS) produced the highest forage Fe, Cu and Zn levels and was equal to compost in elevating corn stover and forage S and the forage B content. The compost produced the highest forage Ca and corn Zn, the AES produced the highest corn Mn, and fertilizer produced the highest forage Mn. None of the amendments produced excessive levels of the above nutrients; rather, the amendments improved the feed quality of the forage and corn stover. Lastly, it was noted that the Mehlich-1 extract only had a significantly positive correlation with forage Cu content.     

加拿大一枝黄花对土壤营养元素吸收与转运特征

选择临海沿江镇加拿大一枝黄花重度入侵区域,分别收集植物与土壤样品,研究加拿大一枝黄花对土壤中7种营养元素的吸收、转运特征。研究结果表明：7种营养元素在植物组织中的平均含量排序为：Zn〉K〉Ca〉N〉Mg〉P〉Mn。而且不同器官对同一种元素的积累存在显著差异,总体规律表现为叶和花蕾积累元素最多,其次是枝条和根状茎,根和茎则积累最少。地上器官对各元素的转移能力表现出明显差异,但各器官均对氮素有较强的转运能力,转运因子均明显高于1。地下器官（根和根状茎）对氮素有较高的富集能力,富集因子同样明显高于1。7种元素在加拿大一枝黄花不同器官的吸收转运存在着一定的促进或者拮抗作用。在花蕾、枝条和根中,磷吸收分别与Mg、Mn和Zn吸收呈现显著负相关;在花蕾中,氮的吸收和Mn的吸收呈现显著正相关;在不同器官里,K、Ca、Mg、Zn和Mn吸收之间多呈现正相关。     

镉胁迫对秋华柳根系活力及其Ca、Mg、Mn、Zn、Fe积累的影响

以秋华柳为试验材料,采用水培试验方式,设置CK(0 mg·L^-1 Cd²⁺)、T₁(2 mg·L^-1 Cd²⁺)、T₂(10 mg·L^-1Cd²⁺)、T₃(20 mg·L^-1Cd²⁺)、T₄(50 mg·L^-1Cd²⁺)5种镉处理浓度,通过对秋华柳根系活力,叶、韧皮部、木质部和根部的镉含量,以及Ca、Mg、Mn、Zn、Fe 5种常规金属元素含量的测定,研究了不同浓度镉胁迫下秋华柳根系活力及Ca、Mg、Mn、Zn、Fe 等金属元素含量的变化.结果表明:1)秋华柳根系活力随着镉处理浓度的增加而逐渐下降,当镉浓度≥10 mg·L^-1时,根系活力与对照相比显著下降.2)随着镉处理浓度的增加,秋华柳叶中Fe的积累受到显著抑制;韧皮部Mg、Mn、Fe的积累受到显著抑制;木质部Ca、Mg、Mn、Zn、Fe 等5种常规金属元素的积累无显著性差异;根部5种常规金属元素的吸收和积累受到显著抑制,表现出镉对其他金属元素积累的拮抗作用.其中,50 mg·L^-1的镉胁迫下,根部Zn的积累量降幅最大,受Cd的抑制最明显.3)各处理组Fe的转移系数与对照相比均无显著性差异;Ca、Mg、Mn、Zn的转移系数均高于对照,且在一定的镉处理水平上差异显著.4)镉胁迫下,秋华柳根部镉的积累量与Ca的积累量呈显著负相关,与其他4种常规金属元素的积累量呈极显著负相关,说明根部常规金属元素的变化可作为秋华柳受镉毒害程度的指示之一.     

Manganese alters mitochodrial integrity in the hearts of swine marginally deficient in magnesium

It was previously reported that pigs marginally deficient in magnesium (Mg) and fed diets high in manganese (Mn) died suddenly with signs of sudden cardiac death. Manganese, which has properties similar to Mg, may exacerbate Mg-deficiency and be accumulated by mitochondria resulting in ultrastructural damage. The objective of this study was to determine whether deaths of the type previously observed were mediated by adverse interactions of Mn and Mg resulting in ultrastructural damage to the myocardium, alterations in electrocardiographic recordings and tissue retention of Mn, Mg and calcium (Ca). Forty-eight pigs were fed one of six diets in a 2 X 3 factorial arrangement of Mg (100 or 1000 mg Mg/kg) and Mn (5, 50 or 500 mg Mn/kg) for 8 weeks. Left ventricle muscle samples were collected for examination by transmission electron microscopy. No differences in heart muscle ultrastructure were observed between pigs fed low and adequate dietary Mg. However, marked myocardial necrosis and mitochondrial swelling were observed in pigs fed high dietary Mn when combined with low Mg. Feeding low dietary Mg elevated minimum (P < 0.01), maximum (P < 0.05) and average (P < 0.001) heart rates. Low dietary Mg resulted in a 55% probability of a ventricular beat being recorded (P = 0.05) and lower Mg (P < 0.02) and Ca (P < 0.04) contents in heart atria and ventricles. These results suggest that high Mn, when fed in combination with low Mg, disrupts mitochondrial ultrastructure and is associated with the sudden deaths previously reported.     

Manganese stimulates calcium flux through the mitochondrial uniporter

Mn2+ alters the balance between the simultaneous uptake and release of Ca2+ across the mitochondrial inner membrane toward a lower external level. Addition of as little as 0.5 microM Mn2+ to energised mitochondria from rat liver, rat heart or guinea-pig brain changed the level at which they buffered Ca2+ in the medium. That extramitochondrial Mn2+ was responsible was suggested by a partial decay in the shift in Ca2+ steady state at a rate similar to the rate at which Mn2+ was accumulated by the mitochondria. The alteration of transmembrane Ca2+ distribution by Mn2+ required that both Mg2+ and Pi be present, and was almost maximal at Mg2+ and Pi levels in the physiological range. Substitution of spermine or Ni2+ for Mg2+, or acetate for Pi, abolished the effect. In contrast to Sr2+, Mn2+ did not inhibit either EGTA- or Ruthenium red-induced release of Ca2+ from the mitochondria. However, when flux through the uniporter was rate-limiting, Mn2+ accelerated Ca2+ uptake. The stimulation showed hyperbolic kinetics, with an element of competition discernible in the Mn2+-Mg2+ interaction. Thus, extramitochondrial Mn2+ at levels occurring in vivo can alter the mitochondrial 'set-point' by stimulating Ca2+ influx through the uniporter.     

微波消解-FAAS法分析并比较旱芹(Apium graveolens L.)不同部位八种金属元素的含量

采用微波消解法处理旱芹根、茎、叶,并用火焰原子吸收法测定其中的Na、K、Ca、Mg、Fe、Mn、Zn、Cu 8种金属元素的含量。结果表明:旱芹中富含人体必需的Na、K、Mg、Fe、Ca等元素,各元素在不同部位含量有一定差异。Fe元素在旱芹根中含量为883.57μg.g-1,明显高于茎和叶;Ca、Zn和Mn元素在旱芹叶中的含量分别为11 103.74,214.04,88.07μg.g-1,明显高于茎和根;K、Na和Mg元素在旱芹茎中的含量高于根和叶中,Cu元素含量在各部位差异不大。方法的加标回收率为96.8%～105.8%,相对标准偏差(RSD)≤3.36%。     

DNA denaturation in situ. Effect of divalent cations and alcohols

Heat denaturation profiles of rat thymus DNA, in intact cells, reveal the presence of two main DNA fractions differing in sensitivities to heat. The thermosensitive DNA fraction shows certain properties similar to those of free DNA: its stability to heat is decreased by alcohols and is increased in the presence of the divalent cations Ca2+, Mn2+, or Mg2+ at concentrations of 0.1-1.0 mM. Unlike free DNA, however, this fraction denatures over a wide range of temperature, and is heterogeneous, consisting of at least two subfractions with different melting points. The thermoresistant DNA fraction shows lowered stability to heat in the presence of Ca2+, Mn2+, or Mg2+ and increased stability in the presence of alcohols. It denatures within a relatively narrow range of temperature, consists of at least three subfractions, and, most likely, represents DNA masked by histones. The effect of Ca2+, Mn2+, or Mg2+ in lowering the melting point of the thermoresistant DNA fraction is seen at cation concentrations comparable to those required to maintain gross chromatin structure in cell nuclei or to support superhelical DNA conformation in isolated chromatin (0.5-1.0 mM). It is probable that factors involved in the maintenance of gross chromatin organization in situ and/or related to DNA superhelicity also have a role in modulating DNA-histone interactions, and that DNA-protein interactions as revealed by conventional methods using isolated chromatin may be different from those revealed when gross chromatin morphology remains intact.     

Determination of major and trace elements in the liver of Wistar rats by inductively coupled plasma-atomic emission spectrometry and mass spectrometry

Inductively coupled plasma-mass spectrometry (ICP-MS) and inductively coupled plasma-atomic emission spectrometry (ICP-AES) were used to determine age-related changes in the concentrations of constituent elements in the livers of Wistar rats of 1 week to 12 months old. At first, sample preparation and analytical conditions were investigated in order to set up a simple routine procedure for measuring multiple elements simultaneously. Seventeen elements in the standard reference samples of bovine and pork livers as well as rat liver samples could be determined with a reasonable precision and reproducibility. They were P, K, Na, Fe, Mg, Ca, Zn, Rb, Cu, Mn, Mo, Al, Co, Sr, Cs, Pb, and Cd in order of the levels of concentration in the adult rat livers. Of these elements, the five major elements (P, K, Na, Fe, Mg, Ca) were determined with ICP-AES and the others with ICP-MS. Although the number of animals was too small to draw a statistically definite conclusion, it seems that age-related changes in the concentrations of these elements could be categorized into three general patterns: (1) remaining essentially constant throughout the animal ages, as observed for P, K, Na, Mg, Ca, Rb, Sr, Cs, and Pb, (2) increasing with age, as observed for Fe, Mn, Mo, Co, and Cd, and (3) decreasing with age, especially in the early stages of growth, as observed for Cu and Zn.