COVID-19 and “natural” experiments arising from physical distancing: a hypothetical case study from chronobiology

ABSTRACT

With countless “natural” experiments triggered by the COVID-19-associated physical distancing, one key question comes from chronobiology: “When confined to homes, how does the reduced exposure to natural daylight arising from the interruption of usual outdoor activities plus lost temporal organization ordinarily provided from workplaces and schools affect the circadian timing system (the internal 24 h clock) and, consequently, health of children and adults of all ages?” Herein, we discuss some ethical and scientific facets of exploring such natural experiments by offering a hypothetical case study of circadian biology.     

Occurrence of two structural types of mercury reductases among Gram-positive bacteria

Structural variants of mercury reductase containing the N-terminal domain, which is easily cleaved by trypsin, have been found in Gram-positive bacteria with a low genomic G + C content (Bacillus, Staphylococcus and, possibly, some other genera). Mercury reductases without the N-terminal domain and relatively resistant to limited proteolysis are typical for Gram-positive bacteria with a high genomic G + C content (Arthrobacter, Citreobacterium, Micrococcus, Mycobacterium, Rhodococcus). Both types of mercury reductase genes may be located on plasmids.     

Energy coupling sites in the electron transport chain of Zymomonas mobilis

Abstract Energy-coupling sites in the electron transport chain of the obligately fermentative aerotolerant bacterium Zymomonas mobilis were examined. The H⁺ /O stoichiometry of the electron transport chain in intact bacteria oxidizing ethanol was close to 3.3. Cytoplasmic membrane vesicles coupled NADH oxidation to ATP synthesis. With ascorbate/phenazine methosulfate they showed oxygen uptake which was sensitive to antimycin A, but no significant ATP synthesis could be detected. Cells with a defective coupling site I, prepared by cultivation on a sulfate-deficient medium, showed a decreased rotenone sensitivity of respiration, and they lacked almost all the respiration-driven proton translocation and ATP synthesis. We conclude that, despite the reported composition of the electron transport chain, only energy coupling site 1 was functional in Z. mobilis .     

Photosynthetic gas exchange and the stable isotope composition of leaf water: comparison of a xylem-tapping mistletoe and its host

Photosynthetic gas exchange and the stable isotopic composition of foliage water were measured for a xylem tapping mistletoe, Phoradendron juniperinum, and its host tree, Juniperus osteosperma, growing in southern Utah. The observed isotopic composition of water extracted from foliage was compared to predictions of the Craig-Gordon model of isotopic enrichment at evaporative sites within leaves. Assimilation rates of juniper were higher and stomatal conductance was lower than the values observed for the mistletoe. This resulted in lower intercellular/ ambient CO₂ values in the juniper tree relative to its mistletoe parasite. For mistletoe, the observed foliage water hydrogen and oxygen isotopic enrichment was less than that predicted by the model. In juniper, foliage water hydrogen isotopic enrichment was also lower than that predicted by the evaporative enrichment model. In contrast, the oxygen isotopic enrichment in juniper foliage water was slightly greater than that predicted for the evaporative sites within leaves. Hydrogen isotopic enrichment in mistletoe foliage shows systematic variation with stem segment, being highest near the tips of the youngest stems and decreasing toward the base of the mistletoe, where isotopic composition is close to that of stem water in the host tree. In a correlated pattern, mid-day stomatal conductance declined abruptly in mistletoe foliage of increasing age.     

Phospholipid dependence of the anion transport system of the human erythrocyte membrane. Studies on reconstituted band 3/lipid vesicles

Band 3 protein extracted from human erythrocyte membranes by Triton X-100 was recombined with the major classes of phospholipid occurring in the erythrocyte membrane. The resulting vesicle systems were characterized with respect to recoveries, phospholipid composition, protein content and vesicle size as well as capacity and activation energy of sulfate transport. Transport was classified into band-3-specific fluxes and unspecific permeability by inhibitors. Transport numbers (sulfate ions per band 3 per minute) served as a measure of functional recovery after reconstitution. The transport properties of band 3 proved to be insensitive to replacement of phosphatidylcholine by phosphatidylethanolamine, while sphingomyelin and phosphatidylserine gradually inactivated band-3-specific anion transport when present at mole fractions exceeding 30 mol%. The activation energy of transport remained unaltered in spite of the decrease in transport numbers. The results, which are discussed in terms of requirements of band 3 protein function with respect to the fluidity and surface charge of its lipid environment, provide a new piece of evidence that the transport function of band 3 protein depends on the properties of its lipid environment just as the catalytic properties of some other membrane enzymes. The well-established species differences in anion transport (Gruber, W. and Deuticke, B. (1973) J. Membrane Biol. 13, 19–36) may to some extent reflect this lipid dependence.     

The implications of function on the origin and homologies of the dipterous wing

Abstract The origin of Diptera, and the homologies of the dipteran wing, are re-examined in the light of recent studies on the flight biomechanics and functional wing morphology of Diptera and of Panorpa. Significant Diptera apomorphies are identified, relevant fossils discussed, and a hypothetical wing ground-plan figured.
The arculus, the modified clavus and the anteroposterior asymmetry of the fly wing seem to be adaptations to a mode of flight in which instantaneous wing pitch and camber are controlled automatically, rather than by muscular action; probably in association with the development of asynchronous power musculature.
Tillyard's Cu2 (=CUP) is believed to be a secondary pseudo-vein, his 1A to be the true CuP and 2A to be 1A.
The late Permian fossil Permotipula Patricia is almost certainly a member of the Diptera stem-group, possibly even of the crown-group. The Mesozoic Laurentipteridae and the Permian Permotanyderidae are other possible, but not certain, stem-group members.     

Some New Aspects of 2 × 2 Table Measures and Their Applications

The paper deals with the analysis of 2 × 2 table measures and describes several new possibilities for applying them. An estimate is given for HELLMICH's asymmetric K-measure and a possible extension of the contingency concept in a special 2×2 case is presented. The concept introduced and the recommended computer application of the 2×2 table measures is supported by new results obtained for the relationship between jaw joint pains and noises examined earlier by F. SCHMID and C. ZSCHEGE. With a larger number of observations the opportunity arises for a deeper analysis of this dental problem using path analysis. The plan of evaluation and the conncetion between the variables examined is illustrated by a path-diagram. The association tables determined on the basis of the (C) values introduced during the examination of jaw joint disturbances using association analysis draw attention to the special role of the left side of mastication. The paper raises ideas for further generalisations and indicates where further research is needed.     

Ca2+ ion reversibly inhibits the cytoplasmic streaming ofNitella

Summary When Ca²⁺, K⁺ or Cl^– was injected iontophoretically into the cytoplasm of intactNitella cell, only Ca²⁺ reversibly inhibited the cytoplasmic streaming. However, when an extremely large current was used, the cytoplasmic streaming was reversibly inhibited irrespective of the ion species. This inhibition may be due to a transient increase of free Ca²⁺.