Phenols and phenol oxidases are involved in cadmium accumulation in the water plants Nymphoides peltata (Menyanthaceae) and Nymphaeae (Nymphaeaceae)

This comparative study investigates the mechanism of cadmium accumulation in the semiaquatic plant Nymphoides peltata (Menyanthaceae) and the aquatic plant Nymphaea (Nymphaeaceae). It was conducted as part of an ongoing study of the use of water plants for phytoremediation. Epidermal structures, known as hydropotes, are located on the abaxial epidermis of the leaf laminae of Nymphoides peltata and are shown to contain phenols, peroxidase and polyphenol oxidase activities. When plants are subjected to 50 mg/l of cadmium in the growth medium, these hydropotes accumulate cadmium. Cadmium-induced increases in phenols, peroxidase and polyphenol oxidase activities were determined in plant extracts. Cadmium binding by polymerized phenols was demonstrated in vivo. In comparison with Nymphaeae epidermal glands, N. peltata hydropotes are larger, open, and create bigger crystal, the latter principally composed of calcium and, proportionally, less cadmium. Although both plants showed similar levels of cadmium accumulation, N. peltata was sensitive while Nymphaeae was resistant to this cadmium level. It is suggested that in these water plants the main mechanism for cadmium accumulation is based on the trapping of cadmium crystals by polymerized phenols in specialized epidermal structures and this is due to peroxidase and polyphenol oxidase activities. Nymphaeae, with greater peroxidase activity and more polyphenols, is more resistant to this heavy metal than N. peltata.     

Dynamic proteomics in individual human cells uncovers widespread cell-cycle dependence of nuclear proteins

We examined cell cycle-dependent changes in the proteome of human cells by systematically measuring protein dynamics in individual living cells. We used time-lapse microscopy to measure the dynamics of a random subset of 20 nuclear proteins, each tagged with yellow fluorescent protein (YFP) at its endogenous chromosomal location. We synchronized the cells in silico by aligning protein dynamics in each cell between consecutive divisions. We observed widespread (40%) cell-cycle dependence of nuclear protein levels and detected previously unknown cell cycle-dependent localization changes. This approach to dynamic proteomics can aid in discovery and accurate quantification of the extensive regulation of protein concentration and localization in individual living cells.     

Disentangling subpopulations in single-molecule FRET and ALEX experiments with photon distribution analysis

Among the advantages of the single-molecule approach when used to study biomolecular structural dynamics and interaction is its ability to distinguish between and independently observe minor subpopulations. In a single-molecule Förster resonance energy transfer (FRET) and alternating laser excitation diffusion experiment, the various populations are apparent in the resultant histograms. However, because histograms are calculated based on the per-burst mean FRET and stoichiometry ratio and not on the internal photon distribution, much of the acquired information is lost, thereby reducing the capabilities of the method. Here we suggest what to our knowledge is a novel statistical analysis tool that significantly enhances these capabilities, and we use it to identify and isolate static and dynamic subpopulations. Based on a kernel density estimator and a proper photon distribution analysis, for each individual burst, we calculate scores that reflect properties of interest. Specifically, we determine the FRET efficiency and brightness ratio distributions and use them to reveal 1), the underlying structure of a two-state DNA-hairpin and a DNA hairpin that is bound to DNA origami; 2), a minor doubly labeled dsDNA subpopulation concealed in a larger singly labeled dsDNA; and 3), functioning DNA origami motors concealed within a larger subpopulation of defective motors. Altogether, these findings demonstrate the usefulness of the proposed approach. The method was developed and tested using simulations, its rationality is described, and a computer algorithm is provided.     

The identification and characterization of osmotolerant yeast isolates from chemical wastewater evaporation ponds

Ramat Hovav is a major chemical industrial park manufacturing pharmaceuticals, pesticides, and various aliphatic and aromatic halogens. All wastewater streams are collected in large evaporation ponds. Salinity in the evaporation ponds fluctuates between 3% (w/v) and saturation and pH values range between 2.0 and 10.0. We looked for microorganisms surviving in these extreme environmental conditions and found that 2 yeast strains dominate this biotope. 18S rDNA sequence analysis identified the isolates as Pichia guilliermondii and Rhodotorula mucilaginosa. Both isolates grew in NaCl concentrations ranging up to 3.5 M and 2.5 M, respectively, and at a pH range of 2-10. There was a distinct difference between the Rhodotorula and Pichia strains and S. cerevisiae RS16 that served as a control strain with respect to accumulation of osmoregulators and internal ion concentrations when exposed to osmotic stress. The Pichia and Rhodotorula strains maintained high glycerol concentration also in media low in NaCl. Utilization of various carbon sources was examined. Using a tetrazolium-based assay we show that the Rhodotorula and Pichia strains are capable of utilizing a wide range of different carbon sources including anthracene, phenanthrene, and other cyclic aromatic hydrocarbons.     

Age-related effects in enzyme catalysis

Summary Rat muscle glyceraldehyde-3-phosphate dehydrogenase is one of several enzymes which have been found to undergo age-related modifications. While the amount of this enzyme in muscle tissue does not change with age, both its specific activity and affinity towards its co-enzyme are significantly reduced in the old tissue.Age-related structural changes were found to exist in the nicotinamide binding site of the enzyme and the reactions leading to the activity loss in old glyceraldehyde-3-phosphate dehydrogenase were shown to involve a reversible modification of the essential cysteine-149 residue at the active site of the enzyme. The aging effects were simulated by a controlled oxidation of cys-149 in samples of young glyceraldehyde-3-phosphate dehydrogenase and subsequent reduction of this residue by 2-mercaptoethanol. The enzyme modified in this way closely resembles native old glyceraldehyde-3-phosphate dehydrogenase, indicating that the structural modifications in the latter enzyme are indeed introduced by a post-translational process. The mechanism for aging of glyceraldehyde-3-phosphate dehydrogenase which is proposed, based on these observations, thus assumes an oxidation of cys-149 as its first step followed by irreversible conformational changes in the enzyme molecule. The aging of glyceraldehyde-3-phosphate dehydrogenase may thus be triggered by the reduced ability of old muscle tissue to protect its constituents against oxidation.Abbreviations CPL circular polarization of luminescence - DTNB 5,5-dithiobis (2-nitrobenzoic acid) - GPDH D-glyceraldehyde-3-phosphate dehydrogenase - ENAD⁺ nicotinamide 1,N⁶-ethenoadenine dinucleotide     

Influence of clay minerals,humic acid and bacterial capsular polysaccharide on the survival of Klebsiella aerogenes exposed to drying and heating in soils

The influence of clay minerals, humic acid and capsular polysaccharide on the survival of Klebsiella aerogenes exposed to drying and heating in soils was investigated. The study of three types of soils showed that the survival of the bacteria was higher in montmorillonitic than in kaolinitic soils. When a sandy soil was amended with 10 per cent montmorillonite, 10 per cent kaolinite or 0.5 per cent humic acid, the survival of K. aerogenes was increased in the presence of montmorillonite but was not affected by kaolinite or humic acid. It was suggested that montmorillinite affected the pattern of water retention by the cells during the drying process. The influence of capsular polysaccharides was also investigated and no significant difference was abserved between the survival of the encapsulated and non-capsulated strains of K. aerogenes exposed to drying and heating in soils. re]19750321     

Effect of montmorillonite and the capsular polysaccharide on the flocculation of Klebsiella aerogenes

A study was undertaken on the effect of colloidal montmorillonite and exocellular polysaccharide produced by Klebsiella aerogenes on the flocculation process of the bacterium.The addition of a low concentration of K-montmorillonite (350 g/ml) led to the flocculation of the non-capsulated strain K₅₄A₃ (0) of K. aerogenes. The volume of the sediment was dependent on the relative concentration of the bacteria and the clay. In contrast with its non-capsulated counterpart, the encapsulated strain K₅₄A₃ was more stable in the presence of a low concentration of K-montmorillonite. The flocculation of the cells was affected by the composition of the growth medium, the suspension being more stable when the bacteria were grown on a rich sugar agar. The addition of capsular polysaccharide to the non-capsulated strain reduced or prevented the flocculation process. These results suggest that the capsular polysaccharide, which contain COO- as sole ionogenic groups, probably attach to and neutralize the positive charges at the edges of the clay platelets. Consequently, K-montmorillonite did not cause any flocculation of the cells when the capsular polysaccharide was present.     

The synthesis of primitive ‘living’ forms: Definitions,goals, strategies and evolution synthesizers

The arbitrariness of the definition of life is discussed in relation to both the archaic biological entities that preceded cells during the Molecular Evolution era, and the hypothetical, primitive, living entities that presumably can be synthesized in the laboratory. Several experimental approaches to the synthesis, detection, and characterization of living entities are discussed. The experimental approaches considered for the synthesis are the constructionist strategy, the whole-environment strategy, and the modular strategy, which is a combination of the first two. The whole-environment strategy is discussed in more detail and the establishment of an Evolution Synthesizer, based on this strategy, is proposed and rationalized. The guidelines for the detection and characterization of populations and processes of living entities include chemical and physical analyses, but are based mainly on the reproductive characterization of these entities. It is expected that the higher the evolutionary level of the living entities, the longer and more difficult it will be to synthesize them, but the easier it will be to detect them.     

Prebiotic nucleotide oligomerization in a fluctuating environment: Effects of kaolinite and cyanamide

Summary The clay kaolinite was tested for its ability to promote nucleotide oligomerization in model prebiotic systems. Heterogeneous mixtures of clay, water and nucleotide were repeatedly evaporated to dryness at 60°C and redissolved in water in cyclic fashion in the presence or absence of cyanamide and/ or ammonium chloride. With or without cycling, kaolinite alone did not promote the oligomerization of nucleotides at detectable levels. Cycling of clay in combination with cyanamide, however, promoted high levels of condensation to a mixture of oligonucleotides and dinucleotide pyrophosphate without requiring ammonium chloride. Although cycling with clay favored synthesis of dinucleotide pyrophosphate, cycling without clay enhanced formation of oligonucleotides. These results support the hypothesis that the presence of clays in fluctuating environments would have influenced the course of prebiotic condensation reactions.     

Light-modulated exposure of the light-harvesting complex II (LHCII) to protein kinase(s) and state transition in Chlamydomonas reinhardtii xanthophyll mutants

Reversible phosphorylation of chl a/b protein complex II (LHCII), the mobile light-harvesting antenna, regulates its association and energy transfer/dissipation to photosystem (PS) II or I (state transition). Excitation of LHCII induces conformational changes affecting the exposure of the phosphorylation site at the N-terminal domain to protein kinase(s) [Zer, H., et al. (1999) Proc. Natl. Acad. Sci. U.S.A. 96, 8277-8282; Zer, H., et al. (2003) Biochemistry 42, 728-738]. Thus, it was of interest to examine whether the pigment composition of LHCII affects the light-induced modulation of LHCII phosphorylation and state transition. To this end, we have used thylakoids of wild-type Chlamydomonas reinhardtii and xanthophyll deficient mutants npq1, lor1, npq2, npq1 lor1, and npq2 lor1. Phosphorylated protein bands P11, P13, and P17 are considered components of the mobile C. reinhardtii LHCII complex. The protein composition of these bands has been analyzed by mass spectrometry using Qtof-2 with a nanospray attachment. P11 and P13 contain C. reinhardtii light-harvesting chlorophyll a/b binding protein LhcII type I. P17 contains C. reinhardtii LhcII types III and IV. Illumination of isolated thylakoids inhibits the redox-controlled phosphorylation of polypeptide bands P13 and P17 and to a lower extent that of P11. The light-induced inhibition of LHCII phosphorylation and the state transition process are not influenced by extensive differences in the xanthophyll composition of the mutants. Thus, LHCII can be visualized as possessing two functionally distinct, independent domains: (i) the pigment binding transmembrane domain regulating the extent of energy transfer/dissipation and (ii) the surface-exposed phosphorylation site regulating the association of LHCII with PSII or PSI.