Additives and Enzyme Stability

The polypeptide chain of an enzyme is folded so that the necessary functional groups are brought together in the active site. Conformational changes may disrupt this arrangement and cause loss of enzymic activity. The effect of soluble additives on the unfolding process is discussed. Additives may be classified as substrates and similar ligands, small uncharged organic molecules, specific and non-specific ionic species, and polymers.     

Effect of dolichyl monophosphate on the permeability properties of lipid membranes

The effect of dolichyl monophosphate on the permeability properties of dimyristoylphosphatidylcholine bilayers to alkaline cations, Ca²⁺ and glucose has been determined by stop-flow spectrophotometry. The results show that, in con trast to free dolichol effects, the monophosphate derivative increased the permeability following a decreasing order of the permeating particle size. Phase diagrams indicate that dolichyl monophosphate is fully incorporated into the phosphatidylcholine bilayer around 0.75% weight/weight ratio. For these ratios, the permeation of ions is higher in the gel than in the liquid crystalline state.     

BioEssays 10/2020

Frequent independent origins of environmental sex determination (ESD) are assumed within amniotes. However, the phylogenetic distribution of sex-determining modes suggests that ESD is likely very ancient and may be homologous across ESD groups. Sex chromosomes are demonstrated to be old and stable in endothermic (mammals and birds) and many ectothermic (non-avian reptiles) lineages, but they are mostly non-homologous between individual amniote lineages. The phylogenetic pattern may be explained by ancestral ESD with multiple transitions to later evolutionary stable genotypic sex determination. It is pointed out here that amniote ESD shares several key aspects with sequential hermaphroditism of fishes such as a lack of sex differences in genomes, biased population sex ratios, and potentially also molecular mechanism related to general stress responses. Here, it is speculated that ESD evolves via a heterochronic shift of the sensitive period of sex change from the adult to the embryonic stage in a hermaphroditic amniote ancestor. Also see the video abstract here https://youtu.be/q2mjtlCefu4 .     

Pollen-based biome reconstruction for southern Europe and Africa 18,000 yr bp

Pollen data from 18,000 ¹⁴C yr bp were compiled in order to reconstruct biome distributions at the last glacial maximum in southern Europe and Africa. Biome reconstructions were made using the objective biomization method applied to pollen counts using a complete list of dryland taxa wherever possible. Consistent and major differences from present‐day biomes are shown. Forest and xerophytic woods/scrub were replaced by steppe, both in the Mediterranean region and in southern Africa, except in south‐western Cape Province where fynbos (xerophytic scrub) persisted. Sites in the tropical highlands, characterized today by evergreen forest, were dominated by steppe and/or xerophytic vegetation (cf. today’s Ericaceous belt and Afroalpine grassland) at the last glacial maximum. Available data from the tropical lowlands are sparse but suggest that the modern tropical rain forest was largely replaced by tropical seasonal forest while the modern seasonal or dry forests were encroached on by savanna or steppe. Montane forest elements descended to lower elevations than today.     

RNA editing of 10 Didymium iridis mitochondrial genes and comparison with the homologous genes in Physarum polycephalum

Regions of the Didymium iridis mitochondrial genome were identified with similarity to typical mitochondrial genes; however, these regions contained numerous stop codons. We used RT-PCR and DNA sequencing to determine whether, through RNA editing, these regions were transcribed into mRNAs that could encode functional proteins. Ten putative gene regions were examined: atp1, atp6, atp8, atp9, cox1, cox2, cytb, nad4L, nad6, and nad7. The cDNA sequences of each gene could encode a functional mitochondrial protein that was highly conserved compared with homologous genes. The type of editing events and editing sequence features were very similar to those observed in the homologous genes of Physarum polycephalum, though the actual editing locations showed a variable degree of conservation. Edited sites were compared with encoded sites in D. iridis and P. polycephalum for all 10 genes. Edited sequence for a portion of the cox1 gene was available for six myxomycetes, which, when compared, showed a high degree of conservation at the protein level. Different types of editing events showed varying degrees of site conservation with C-to-U base changes being the least conserved. Several aspects of single C insertion editing events led to the preferential creation of hydrophobic amino acid codons that may help to minimize adverse effects on the resulting protein structure.     

Spatial productivity variations during formation of sapropels S5 and S6 in the Mediterranean Sea: evidence from Ba contents

We investigated five time-equivalent core sections (180-110 kyr BP) from the Balearic Sea (Menorca Rise), the easternmost Levantine Basin and southwest, south, and southeast of Crete to reconstruct spatial patterns of productivity during deposition of sapropels S5 and S6 in the Mediterranean Sea. Our indicators are Ba, total organic carbon and carbonate contents. We found no indications of Ba remobilization within the investigated core intervals, and used the accumulation rate of biogenic Ba to compute paleoproductivity. Maximum surface water productivity (up to 350 g C/m²/yr) was found during deposition of S5 (isotope stage 5e) but pronounced spatial variability is evident. Coeval sediment intervals in the Balearic Sea show very little productivity change, suggesting that chemical and biological environments in the eastern and western Mediterranean basins were decoupled in this interval. We interpret the spatial variability as the result of two different modes of nutrient delivery to the photic zone: river-derived nutrient input and shoaling of the pycnocline/nutricline to the photic zone. The productivity increase during the formation of S6 was moderate compared to S5 and had a less marked spatial variability within the study area of the eastern Mediterranean Sea. Given that S6 formed during a glacial interval, glacial boundary conditions such as high wind stress and/or cooler surface water temperatures apparently favored lateral and vertical mixing and prevented the development of the spatial gradients within the Eastern Mediterranean Sea (EMS) observed for S5. A non-sapropel sediment interval with elevated Ba content and depleted ¹⁸O/¹⁶O ratios in planktonic foraminifer calcite was detected between S6 and S5 that corresponds to the weak northern hemisphere insolation maximum at 150 kyr. At this time, productivity apparently increased up to five times over surrounding intervals, but abundant benthic fauna show that the deep water remained oxic. Following our interpretation, the interval denotes a failed sapropel, when a weaker monsoon did not force the EMS into permanent stratification. The comparison of interglacial and glacial sapropels illustrates the relevance of climatic boundary conditions in the northern catchment in determining the facies and spatial variability of sapropels within the EMS.     

Seasonal changes of the ultrastructure of the pars tuberalis of the hypophysis of Rana temporaria

Summary In the pars tuberalis of the hypophysis of Rana temporaria, which shows the ultrastructural characteristics of a polypeptide hormone secreting endocrine gland, seasonal changes of the ultrastructure are described. In accordance with the literature, these seasonal changes of ultrastructure are interpreted as the morphological expression of seasonal changes of endocrine activity of the pars tuberalis.     

When corridors collide: Road-related disturbance in commuting bats

As an increasingly dominant feature in the landscape, transportation corridors are becoming a major concern for bats. Although wildlife–vehicle collisions are considered to be a major source of mortality, other negative implications of roads on bat populations are just now being realized. Recent studies have revealed that bats, like many other wildlife species, will avoid roads rather than cross them. The consequence is that roads act as barriers or filters to movement, restricting bats from accessing critical resources. Our objective was to assess specific features along the commuting route, road, or surrounding landscape (alone or in combination) that exacerbated or alleviated the likelihood of a commuting bat exhibiting an avoidance behavior in response to an approaching vehicle. At 5 frequently used commuting routes bisected by roads, we collected data on vehicles travelling along the roads (such as visibility and audibility), commuting bats (such as height), and composition of the commuting route. We revealed that commuting route structure dictated the frequency at which bats turned back along their commuting routes and avoided the road. We found that gaps (>2 m) in commuting routes, such as the road itself, caused bats to turn away just before they reached the road. Furthermore, we found that turning frequencies of bats increased with vehicle noise levels and the locations at which bats responded to vehicles corresponded with areas where noise levels were greatest, including gaps <2 m. This suggested that bats had a disturbance threshold, and only reacted to vehicles when associated noise reached a certain level. We found that threshold levels for our study species were approximately 88 dB, but this value was likely to vary among species. Thus, our findings indicate that restoring (e.g., replanting native trees and shrubs in gaps) and establishing commuting routes (such as planting tree-lines and wooded hedgerows), as well as creating road-crossing opportunities (such as interlinking canopies) will improve the permeability of a road-dominated landscape to bats. Furthermore, our study highlights the influence of the soundscape. We recommend that effective management and mitigation strategies should take into account the ecological design of the acoustic environment. © 2012 The Wildlife Society.     

Temperature-Sensitive Behavior of Paramecium caudatum

SYNOPSIS. The effect of temperature on the behavior of swimming cells of Paramecium caudatum has been investigated by photographic analyses of their tracks in uniform temperature, in temperature gradient, or in temperature changing with time. When the cells were placed in the temperature gradient, the frequency of discontinuous directional changes of cells swimming toward the optimal temperature, the temperature of the culture, was much lower than that of the cells swimming in the opposite direction. This difference in the frequency of directional changes explained the observed accumulation of the cells at - the optimal temperature. When the temperature was suddenly changed toward the optimum, a transient decrease of the frequency of directional changes was observed and when the temperature was changed in the reverse direction, a transient increase of the frequency was noted. This transient response to the temperature change was the origin of the dependence of the frequency of directional changes on the swimming direction in the temperature gradient. Finally, the relation between the magnitude of the transient response and the rate of the temperature change was derived.