A theory of atmospheric oxygen

Geological records of atmospheric oxygen suggest that pO₂ was less than 0.001% of present atmospheric levels (PAL) during the Archean, increasing abruptly to a Proterozoic value between 0.1% and 10% PAL, and rising quickly to modern levels in the Phanerozoic. Using a simple model of the biogeochemical cycles of carbon, oxygen, sulfur, hydrogen, iron, and phosphorous, we demonstrate that there are three stable states for atmospheric oxygen, roughly corresponding to levels observed in the geological record. These stable states arise from a series of specific positive and negative feedbacks, requiring a large geochemical perturbation to the redox state to transition from one to another. In particular, we show that a very low oxygen level in the Archean (i.e., 10^?7 PAL) is consistent with the presence of oxygenic photosynthesis and a robust organic carbon cycle. We show that the Snowball Earth glaciations, which immediately precede both transitions, provide an appropriate transient increase in atmospheric oxygen to drive the atmosphere either from its Archean state to its Proterozoic state, or from its Proterozoic state to its Phanerozoic state. This hypothesis provides a mechanistic explanation for the apparent synchronicity of the Proterozoic Snowball Earth events with both the Great Oxidation Event, and the Neoproterozoic oxidation.     

A specific arginase-based assay for l-canavanine in leguminous plants

A convenient method for the analysis of free l-canavanine in leguminous plants is described. Canavanine was specifically hydroloyzed to canaline and urea by the enzyme arginase (EC 3.5.3.1). The resulting amino-oxy functions of canaline were measured based on their ability to bleach the yellow colour of pyridoxal 5′-phosphate. Canavanine in the seeds of Canavalia ensiformis was determined with this method.     

Oxovanadium(IV) complex formation by simple sugars in aqueous solution.

The binding of oxovanadium(IV) to simple sugars in neutral or basic aqueous solution, as studied by EPR and electronic absorption spectroscopy, is reported. The complexation is favored in basic media and involves the coordination of the metal ion to couples of adjacent deprotonated hydroxyls of the sugar molecule. However, only the ligands provided with cis couples can adopt this chelating ligand behavior. The ability of the cis hydroxyl couples to yield chelated complexes has been related to the structural rearrangement (decrease of the O-C-C-O torsion angle in the five-membered chelated ring) needed to permit the oxovanadium(IV) coordination by the sugar molecule.     

Multi‐modal meta‐analysis of cancer cell line omics profiles identifies ECHDC1 as a novel breast tumor suppressor

Molecular and functional profiling of cancer cell lines is subject to laboratory‐specific experimental practices and data analysis protocols. The current challenge therefore is how to make an integrated use of the omics profiles of cancer cell lines for reliable biological discoveries. Here, we carried out a systematic analysis of nine types of data modalities using meta‐analysis of 53 omics studies across 12 research laboratories for 2,018 cell lines. To account for a relatively low consistency observed for certain data modalities, we developed a robust data integration approach that identifies reproducible signals shared among multiple data modalities and studies. We demonstrated the power of the integrative analyses by identifying a novel driver gene, ECHDC1, with tumor suppressive role validated both in breast cancer cells and patient tumors. The multi‐modal meta‐analysis approach also identified synthetic lethal partners of cancer drivers, including a co‐dependency of PTEN deficient endometrial cancer cells on RNA helicases.     

Inhibition of soybean lipoxygenase-1 by 10-butyryl substituted 1,8-dihydroxy-9-anthrone (butantrone)

10-Butyryl substituted 1,8-dihydroxyanthrone (butantrone) inhibited soybean lipoxygenase-1 irreversibly and more efficiently than its parent compound 1,8-dihydroxyanthrone (dithranol, anthralin) (IC50 values 0.090 mM and 1.1 mM, respectively). Intact butantrone rather than its hydrolysis product was the primary effector and the 10-butyryl moiety its site specific probe, probably directing the inhibitor to the proximity of the binding site of the lipid substrate/product.     

Interaction of VO ion with human serum transferrin and albumin

The complexation of VO²⁺ ion with the high molecular mass components of the blood serum, human serum transferrin (hTf) and albumin (HSA), has been re-examined using EPR spectroscopy. In the case of transferrin, the results confirm those previously obtained, showing that VO²⁺ ion occupies three different binding sites, A, B₁ and B₂, distinguishable in the X-band anisotropic spectrum recorded in D₂O. With albumin the results show that a dinuclear complex (VO)₂^dHSA is formed in equimolar aqueous solutions or with an excess of protein; in the presence of an excess of VO²⁺, the multinuclear complex (VO)_x^mHSA is the prevalent species, where x = 5-6 indicates the equivalents of metal ion coordinated by HSA. The structure of the dinuclear species is discussed and the donor atoms involved in the metal coordination are proposed on the basis of the measured EPR parameters. Two different binding modes of albumin can be distinguished varying the pH, with only one species being present at the physiological value. The results show that the previously named “strong” site is not the N-terminal copper binding site, and some hypothesis on the metal coordination is discussed, with the ⁵¹V A_z values for the proposed donor sets obtained by DFT (density functional theory) calculations. Finally, preliminary results obtained in the ternary system VO²⁺/hTf/HSA are shown in order to determine the different binding strength of the two proteins. Due to the low VO²⁺ concentration used, the recording of the EPR spectra through the repeated acquisition of the weak signals is essential to obtain a good signal to noise ratio in these systems.     

Selective inhibition of carbonic anhydrase IX and XII by coumarin and psoralen derivatives

A small library of coumarin and their psoralen analogues EMAC10157a-b-d-g and EMAC10160a-b-d-g has been designed and synthesised to investigate the effect of structural modifications on their inhibition ability and selectivity profile towards carbonic anhydrase isoforms I, II, IX, and XII. None of the new compounds exhibited activity towards hCA I and II isozymes. Conversely, both coumarin and psoralen derivatives were active against tumour associated isoforms IX and XII in the low micromolar or nanomolar range of concentration. These data further corroborate our previous findings on analogous derivatives, confirming that both coumarins and psoralens are interesting scaffolds for the design of isozyme selective hCA inhibitors.     

Update on the presence of taste buds on the laryngeal surface of the epiglottis]

Previous investigations have ascertained, according to the results obtained by Bradley et al. (1980) in the sheep, that the laryngeal surface of the epiglottis of goat and bovine is always provided with numerous taste buds. These observations have verified in other ruminant species, as the moufflon and the buffalo, the validity of the above-named datum and have ascertained that it is always inconstant in the other animal species considered (wild boar, coypu). These taste buds show a typical structure (diameter of the outer taste pore varying from 2.7 to 4.2 micron, width of the chemoreceptors varying from 30 to 60 micron and length from 27.5 to 57.5 micron). Moreover, the normal structure of the above-named taste buds is also testified by the arrangement of their innervation and particularly by the integrity of the synaptic contacts. The results of the present research have permitted a critical and more severe examination of the probable functional role of those laryngeal receptors. In fact, in the ruminants they may protect the deep airways precluding to food particles the larynx in the phase of food regurgitation.     

The effects of UV-B radiation on epidermal anatomy in loblolly pine (Pinus taeda L.) and Scots pine (Pinus sylvestris L.)

The effects of enhanced UV‐B radiation on the needle anatomy of loblolly pine (Pinus taeda L.) and Scots pine (Pinus sylvestris L.) were studied in the field under supplemental UV‐B radiation supplied by a modulated irradiation system. The supplemental UV‐B levels were designed to simulate either a 16 or 25% loss of stratospheric ozone over College Park, Maryland. Enhanced UV‐B radiation caused different responses in these two species. The needles of loblolly pine had larger amounts of tannin in the lumen of epidermal cells and more wall‐bound phenolics in the outer epidermal walls of UV‐B‐treated needles, whereas the most pronounced effect on Scots pine needles was increased cutinization. In both species, the outer epidermal cell walls thickened and the needle cross‐sectional and mesophyll areas decreased (statistically significantly only in Scots pine). This suggests that more carbon may have been allocated to the protection mechanisms at the expense of photosynthetic area. The difference in response between these species suggests that the response to UV‐B radiation is not mediated by a single mechanism and that no generalization with regard to the effects of UV‐B on conifers can be made.